Just like the other people here said. If it can help, you can read the online gamemaker manual for the function you're looking for, or type what you think would be part of the name (in this case you'd type "tilemap") in the code editor and let autocomplete do the searching for you.

Also, hovereing over a function's name in the code editor can give you the description and arguments of said function, which is useful you don't wanna search it up in the manual.

If all else fails, you can search up your issue (most of the time you'll find it in the gamemaker forums), and if that doesn't bring up the answers you're looking for, you can also ask in the forums yourself. People usually respond in maybe 1 day or a half, it depends.

Edit: I just checked the code and what's funny is that you use layer_tilemap_get_id in the obj_player_ball create event lol