Can some help me with overlays?

can someone just give me a quick overlay 101 and allow me to ask questions? i’m so bad at overlays and i just don’t get it ://

Ok you need help on overlays what kind you know like Cars,Desks what is it?

i created an explosion overlay and i wanted it to appear on a black screen i’m changed the sizes and all that but it won’t appear on the screen its just black. i tried to add layers but it still won’t appear

My tip for you if it works or not create your Animate your explosion most episode writers do use there’s animated and i used to feel so annoyed but watch this video it might help if not come chat with me ok!