I already saw lots f people saying that I can use the Assets for any kind of project in unity, but there are some other that say that I just can use Assets if I’m using Unity Pro.
Assets are any file that you use in your game. This can include sound, music, art, code, 3d Models, etc. That being said, it would be quite silly indeed if you could not use assets in the free edition of Unity, because you wouldn’t be able to much of anything.
Short answer, yes, you can use Assets in your game.
There are some Assets in the Unity store that include certain code or effects that can not be used in the free edition. For this reason, those assets in the store normally are clearly labelled that they can not be used with Unity free. In general, as long as the Asset doesn’t say that it can’t be used, it’s usually safe to assume that you can use it.
Unity does offer some sort of refund policy in case you purchase an asset and then discover that you can not use it in the free edition of Unity.