Usually the person referred to, so patronisingly, is the person who undoes your cock-ups for free.
IT is a massive field and there is no one out there, anywhere, capable of knowing everything about any individual specialism, never mind all of it. The IT illiteraty, who provide most of the work to those they refer to as gurus, use the term to describe those willing to make an effort to understand some aspect of PC, network, telephone or general gadget use, often involving no more than reading a manual.
You will often see angry responses on forums from 'experts' to 'newbies' who haven't even RTFM, unsurprisingly. So that is the first piece of advice on this page - RTFM, even if it's going to take you all day. It's your gizmo, learn to use it properly before you trouble somebody else or before you switch it on!
Before you do anything else, use your eyes (or appropriate aids) to read all of this page. Spotted the 'trust no-one' menu link? Use it, now, then come back here when I've written something worth reading.