A digital release must be available for full download in order to be added as a fully-fledged entry to the discography section. Do not add streaming-only releases, such as Youtube uploads, Spotify releases or SoundCloud/Bandcamp/etc. streams without a download option.
Be careful with adding digital singles. They are a somewhat complicated and invidious affair and when they should or should not be added as their own entries is not something that comes with one clear answer. Please check this post (and the thread/subforum in general) for more details and make sure to ask there (or contact a staffer) before adding anything you're not sure about.
Do not add video singles uploaded to Youtube (or elsewhere) as single entries with the release category "Video". This ties in with the first point.
Be wary of digital release dates, even (or rather especially) if given by the band themselves. Many times the "release dates" either are the date something was first recorded (resulting in download releases from 1988 and other absurdities), reflect the release date of a later (or earlier), "more official" physical release, are more or less random or constitute some other kind of misleading info. Be particularly careful with Bandcamp dates. Of course, that doesn't mean that the official given date is always wrong, but it serves to not always take it at face value. For our purposes, a digital album's release date is when it was first made available for official, public, complete download. If you can't be reasonably certain, simply omit the date (this is only possible for version entries connected to a main album), broaden it (i.e. omit month and/or day if you're sure about the year) or keep the album to the additional notes only (with a note about the unknown/uncertain release date).