Recently, I acquired an Ibanez XPT700 (Xiphos).
The guitar is beautiful, the action is perfect, and the pickups are powerful. However, I have absolutely no idea where to start in terms of tone and sound though, as I only have a 45-watt Marshall amp.
How do I start learning about different sounds and effects? I have no knowledge of pedals, amp kinds, and other stuff (except guitar pickups, etc).
I want to get a new amp, maybe some pedals. How did you guys achieve your tone, and how did you learn? Did you guys just go to Guitar Center and test everything out? I really need some guidance here. All I want is to be able to alternate from a sharp thrash-tone to a thick, heavy death metal tone, no black metal for me.

Any tips would he extremely helpful.

Get a tube amp if your amp is not already tube, because solid state amps sound very sterile, and though you might be going for that sound (Dying Fetus for example use Ampeg VH 140C's), they sound bad most of the time and wont get you that heavy giant tone. A word of warning, tube amps are incredibly loud above "1" and if you live in an apartament with cranky neighbours you might have trouble playing one, so if that is the case get some modeling stuff like Line 6 Pod or Axe FX if you got more money, both can emulate tube amps pretty decently but need a lot of tweaking. In my opinion, dont even bother with distortion pedals because most of time, they are intended to drive a clean channel and most of them sound decent at best, while we want good, and even great, right? Maybe a tubescreamer or overdrive for boosting a tube amp for more gain, but also a change in tone. Delays, flangers etc are not worth your time at the moment, only when you are already pretty happy with your tone buy them for effects on leads or riffs (A plus for Line 6 Pod and Axe FX, they aren't just modeling amps, they have got a lot of pretty good effects inside). You might consider a noise gate if your amp is very noisy, and this is usually the case with high gain amps.

So, here is a list of good tube amps for metal:

Peavey 6505+, 6505, 5150 II etc. (Mostly for modern tones, can pull out really heavy shit)
Mesa Double and Triple Rectifier (Good all round, death metal, thrash metal etc.)
Marshall JCM 800 (This one is good for old school tones, Carcass, Morbid Angel etc.)
Orange amps (Good for doom metal)

And modeling stuff:

Axe FX I and II
Kemper Profiling Amplifier
Line Pod 6 (This one is the cheapest here, but still decent on budget)

Most of these amps are heads, so you'd have to buy a cab additionally to it, i'd recommend:
Mesa Rectifier Cabs
Vader Cabs (Now only can be bought used since the company doesnt make them anymore)
Marshall 1960 Cabs

Good luck.

Don't shit on all solid states cause there are quite a few excellent ones that just stomp the shit out of tube heads.

I put up Ampeg SS150 & SS140's, Randall RH100 & RH200, and Sunn Concert Leads above any tube amp esp anything that was made post 1985

As far as getting a good tone from your amp, don't immediately scoop it like a lot of people do. Start with all your tone knobs at halfway, and your gain around there also. Start playing for a bit and getting a feel for the tone of your amp, then slowly dial your gain up a bit at a time. Once you have enough gain, dial it back just a touch. It'll be just as heavy, but a tad more clear - especially if you're going to use it for recording. Then go for your tone controls. Slowly increase or decrease them one at a time, just a bit at a time. Don't scoop out all the midrange, either. Yeah it sounds kinda cool initially, but all the body of the guitar tone is in the midrange, and without that you can't really punch through anything. On my Engl I have my tone settings at roughly: Low 4 low mid 4 high mid 6 high 7 gain 9. (assuming 1-10) and my bugera I have low 4 mid 4 high 7 gain 7 and I think the presence is around 6 or 7.

I had an old solid state Crate 4X10 120 watt combo when I was in high school, can't remember exactly what kind other than it was a crate. Loud as all hell, but couldn't really play heavy metal. There's always ways around that! My guitar had (has) very high output pickups, which helped. I also put an EQ pedal in the effects loop to boost the overall signal a bit. It wasn't much, but it was perfect for a high schooler's budget and that little boost really helped brighten the amp and get a bit more gain out of it, enough that it was capable of metal.

Sorry, kinda got on a rant there.

Okay, if you're asking about amps specifically as in which one to buy, you're going to have to try a bunch out. Darkwolf gave a lot of good recommendations for amps, you can't really go wrong with any of those. Also check into Bugera. Some of their first ones had some reliability problems but they've fixed that and now they're awesome. Incredibly loud and powerful, all tube sound, and affordable. I have the 6262 and it is a tone monster. Check eBay for used amps also, you can find some really good deals on there. Just don't get in a hurry and buy the first amp you come across that you like, be patient and wait for the right one.

I echo what infinite is saying, especially about not immediately going for the scoop, and dialing back the gain just a touch.

I know some people find that counter-intuitive (this *IS* metal, right? dialing back the gain?!?)

But yea, crunch isn't the same as distortion, and being tight is also really heavy. It's harder to be clear and concise when there's noise all over your signal. Also, some amps are "voicing" their tone controls for a scoop anyway, so taking out all the midrange just makes it sound empty.

Mostly, remember that the guitar is part of a total band's soundscape. What sounds really good alone might not sound as good with the rest of the band. Guitars are midrange instruments (not bass and not high treble), and they take up a ton of sonic bandwidth when distorted.

I haven't played a Bugera, but I'll give one a whirl some time. I bought a Laney Ironheart recently and don't particularly care for it (it's not terrible, but not great - it is reasonably priced). My mains are Engl Straights, and I adore them. I've played a ton of amps over the years, and there's really no substitute for just using stuff and seeing what you like.

As long as there's some grit in your chugging, there's enough gain already. Heaviness comes from your hands, don't rely on gear as the be all and all.

cannot agree with this more. this is some of the best advice in this thread thus far.

aside from that, i think it's very dangerous to be looking for the "right sound" for your guitar. there is no one metal guitar tone: try some gear out and figure out what YOU like. taking inspiration from other musicians is definitely good, but if you strive to completely copy another band's guitar sound you'll always fall a bit short. dont' forget that a lot of the guitar tone you hear on any given album has been processed/altered/whatever to some degree in the course of recording and mixing. in the end, it's about playing guitar and figuring out what suits your tastes and needs.