When I first started as a graphic designer,I struggled with overlays quite a lot (Like, A LOT, I actually tried to crop the pictures to fit into the overlays) so I suppose you will too,here is how do you actually use them.
WHAT YOU WILL NEED :
-Your graphic of choice
Step 1 - chose your Overlay.
There is a lot of Overlays on Google,you just need to search for the right words.I usually search for Wattpad cover overlay .
Step 2 - open picsart
I prepared a graphic before hand(feel free to ask me for one)
Step 3- Open your Overlay
Step 4 - drag your Overlay so it fits your liking.
Step 5 - selecting the Overlay,click on blend and scroll to screen
Step 6 - and there you have it,just add the title and the author and you are ready to go.