edragonpein, hi!

All art on OpenGameArt is free to use. But beware of anti-DRM-wavier of CC-type licenses (you might have problems with publishing it on Play Store).

Usually, you can freely pick any licenses you want, but you need to keep track of them (i.e. save license.txt with all files you download) to give credit to the authros if required by the license like CC-BY. Moreover, OpenGameArt requires to link back to the download page for the art (probably in the same license.txt).

@edragonpein:  Welcome aboard!   

 eugeneloza hit it pretty well, the idea is for all the art on here to be free to use but there are some caveats:

CC-BY license has a prohibition on using 'technilogical measures' to restrict distribution.  This is a widely interpretted as a restriction on using CC-BY work on games that are sold/distributed on platforms that require/use DRM.  There's alot of debate on what constitutes DRM and which platforms use or don't use DRM, so generally I would advise you to avoid CC-BY works unless you are distributing a DRM-free PC game (eg. a game where you directly distribute a .exe installer yourself either on your own web site or on a DRM-free store like itch.io, etc).   But that's my 'better safe than sorry' advise, not everyone agrees with it ;)

CC-SA license shares CC-BY's anti-DRM clause but also requires you to re-share any derivative artwork you make under the same license.  I'd encourage you to do this anyway no matter which license the source work uses, it's the best way to say 'thank you' to the artists that posted the original work(s).  Note that you don't need to re-share EVERY derivative work you make, the restriction is actually just that IF you distribute derivative work you must do so under the same license.  So, if you make derivative work and distribute it as part of your game you must license the derivative artwork as CC-BY.  But if you just make some derivative work and keep it on your own hard drive, you don't have to share it.

GPL 2.0/3.0 licenses are also subject a good bit of debate as to what they limit/don't limit you from doing and if they do/don't require you to distribute your game source code.  Generally, I would advise you stear clear of them unless you are explicitly making an Open Source game.

OGA-BY is a new license created by this site with the explicit intent of being CC-BY w/o the 'technical measures' clause.  So works under this license are generally safe to use so long as you credit the original artist.

CC0 is essentially public domain.  Works under this license are absolutely free to use as you please, although it's still a good idea to credit the original artists (unless they explicitly ask not to be credited!)

So my 'better than sorry' summary would be, for commercial work, stick to CC0 and OGA-BY works.  For open source stuff, no limits!  Again, that's just my opinion on the matter, not everyone agrees.

Final note, if a work lists two or more licenses, you may choose to use the work under whichever of the listed licenses you prefer.   So if the submitter checks OGA-BY and CC0 and GPL, you can choose to use the work under terms of GPL.  Or you may choose to use it under the terms of OGA-BY.  Or you can choose to use it under the terms of CC0, it's up to you.

Sorry to hear you found the site/submission FAQ confusing on the topic, I have personally started a Feedback forum thread to try and get a few changes to site docs to help clarify common questions/problems with submissions.   Any details about which parts you found confusing or info you'd like to see added or how it could be better presented would welcome.