Can you explain in very simple terms how this is done?

What I mean is a step by step guide through every single step of the process, i.e. where you go, what you click on?

I am just a starter and such general phrases are actually terribly confusing to me. Even the English. For example:

download and import ThomasV's key on GPG4Win

Does this mean on the platform which is GPG4Win? Or does it mean download to GPG4Win?

I would be very grateful if someone could point me to a guide which takes me through every single step of the process in as much detail as possible, preferably with pictures or in an online video. Also, one which includes everything, so I cannot be told: why did you not do that??? Answer: because I didn't know!