Only the most basic stuff needed

edit

I installed sage years ago, and it worked with simple computations like sum from to .. combinations of well known functions.

Now I seem to have forgotten totally how to use it. As I remember I only used comand line, not sure if inside sage, or the usual terminal of this linux system.

So I need to get the most basic info.

1. How to Sage install on linux (maybe not needed, because it was installed)
2. How to run it.
3. How to type a command to make a basic computation.

I can't see anything anywhere which resembles math. I only see computer instructions which seem to be written for CS experts.