Can someone please explain to me how to locate grass, rocks, trees. dropoffs, etc. on a fish finder. me and my dad just bought a boat and are new to lake fishing and I can't find anything anywhere else on the internet.

Grass can look like a bunch of lines to almost a false bottom depending on how thick and what kind.
Rocks- don't fish many lakes with a lot of rocks
Trees- can have many different shapes depending on if its standing or if its a layover.
Best advice get on you tube they have some good instructional videos.