You can also install it from the terminal. Find the instructions on this page:
By the way, when you take a screenshot, it saves automatically to Pictures in the Home folder. You’ll need a file browser. I use nemo, which works great. Others use nautilus.
Or you can cd to Pictures in the terminal to get them.
Edit: Actually, just install librem5-goodies from the terminal. I had the “-” in the wrong place.