Just hit the “Y” key and then the “Enter” key to continue.
GIMP is already installed, but it won’t hurt to install the extra plugins 
The terminal (command line) is similar to CMD (Command Prompt) in Windows … but massively more powerful.
You can install things through your package manager … but it’s easier for me to type a command on this forum
Hi Millie
The Gimp is the best replacement to Photoshop.
Raw files are a different issue though. Some of the Linux Raw convertors do not support tbe latest cameras and can often give strange results. If your camera shoots raw then it will have come with Raw convertor software. This will be in the form of Windows and Mac programs. Some of these can be coaxed to work in Wine a Linux program that can run certain Windows programs. There people on here that will be able to help you with this.
There is an unofficial Photoshop 5 program that can run in Wine but due to laws governing pirated software I cannot condone or encourage people to source it. It does not process Raw files either.
What camera do you have and what level of photo processing do you require? For instance are you Pro or high end enthusiast?