[She turns the corner right into the cafe's back half and slips into one of the booths, standing beside the chair in a way that suggests he should sit.]

A computer is basically a "computing device". It stores numerical values in a format too small and dense for humans to naturally read, and does equations much faster than humans could ever naturally manage. Since you can represent all kinds of things with numbers, that basic function can cover a lot of ground...

[You thought it was a bad idea...but it's actually just computers 101! She's thorough, but not patient. How quick a student is Kliff?]