Hello, newbie here and to GIMP. Was trying to combine two photos but had difficulty when opening second photo via "Open As Layer". This photo is of my wife and I and was taken professionally. It is something like 4000 X 2000 pixels and when it loaded onto my image board, our heads and legs were not visible and I could not figure out how to resize it. Sorry if I'm not on the correct forum, this is my first post. Help please.

You would do an [Image] [Fit Canvass to Layers].

You could then scale layers visually using the scale tool in the toolbox.

If you want to combine both photos as one photo do it this way (You will need G'MIC)
Open the larger photo first. Then open the other as a layer
Open G'MIC - category 'Arrays and Tiles' go down to Montage
For input layers dont for get to put 'all'
Merging Mode - 'Scaled' will make the largest photo the same size as the smallest in height or width whether you do horizontal or vertical
Up to you if you want borders or padding.

Got it! Thanks.