How do you use GIMP to add color and special effects to old photos?

I'm running Windows 11 and Gimp 3-0. I've been trying to work on some old pictures I found of my late father from when he was in the army. The photos are black and white and I've been scanning them into the computer. That's all working fine, but editing them is overwhelming. I want to add color and some nice effects but I'm lost. I found a tutorial by an artist and game developer Timothy Courtney that demonstrates but my results are not as good. Does anyone here have experience with coloring old photos? What are best practices for someone who is not an artist. Please explain to me step by step like I'm a third grader. Any advice would really help.

This seems to be a useful tutorial.