I have a simple question id like to ask, someone reply please. Asap

[94_SlammedZ28]

Im trying to post a fs ad for my wheels, but how do i put the pictures from my computer into my ad with the info text? everytime i try to add attatchments it keeps saying my picyures are too big. but i see ads with huge pictures in them. Please help me out, i feel like a dumbass