Although I don't listen black and death that much, I wonder what are the differences between them

Listen to both more, then. It's really obvious.

use the googlez and wikipedia to figure it out

There are differences in many areas. Lyrical themes, production styles, song structure, vocals, instrumental techniques, riffing methods, image. Quite a lot, really.

this

Death metal has a higher standard for musicianship

Death Metal: http://www.youtube.com/watch?v=D5Hv0tsvpyU

Black Metal: http://www.youtube.com/watch?v=32n1AK6o5i0

Note: I didn't put thought into these, just 2 random Death and Black Metal videos.

If you're not sure which bands would be examples of which style, use this website's advanced search function (available from the left panel on the front page) to search groups by genre. Alternately, you could look at the massive genre lists. Hybridization styles complicate the whole matter, of course, but in general terms, all you need to do is listen to a few bands.