I want to insert an image into my level and place it on top of a box. How would I go about doing that?
Place a box in the level, and drag-drop a texture or material on top of it.
wait what. No like say I have a pic of a logo that I want to display on some rectangular thing on the wall and make it look like a poster or something, how do i put the pic on it? How would i convert the pic into a texture or material?
You can literally do that 
A box goes in:
You drag and drop an image and material is automagically created:
You may need to adjust UV in the bottom right.
There are other ways. But judging by the description, that’s what you want, no?
If it’s a poster, use a plane instead of a box. Or a very flat box.
If you want more control, create a material in the Content Browser, add a Texture Sample and then apply it to a static mesh of your choice. Either manually from the details panel of that mesh, dynamically from the graph or via drag & drop.
ohh lol. Thanks!