I need to lay a premade grid (jpg) over another photo but can't find a way to load both of them onto one project. It just wants to open it as an new project and and i need to have both jpg's in the same project on different layers. Is there a way to do this? I've tried dragging the second file into the project etc.

I think the easiest way to do that is open your main image as the new document. Then take your grid image on your computer and drag it into Krita. You should get a few options. One of them should be add as new layer. That should take care of it.