Chromatic Tuner Help!

Hi guys,

I am a newbie to guitar. I joined the site to learn. First things first I'd like to tune my guitar and since my ear is not that great I decided to go for a chromatic tuner. Any help would be appreciated.

I bought a SEIKO SAT 500. I have been reading tons of theory, but there is something I'm missing about how chromatic tuners work (and other tuners work in general).

I looked for help sites on the Net and pretty much every site that talks about tuning says to just get a chromatic tuner and it will do all the work. Not quite.

The tuner has the following settings (btw their guide is crap I must have read it 10 times):

Mode (auto and manual)
Pitch (I kept the standard 440hz)
Key
Note

My undestanding:

Modes:
Auto: You play and it tells you which note it is.
Manual: You choose the note and the tuner tells you if it's ok or too flat so you tune it.

Key: Choices are Eb, F, Bb, C. I read the theory for beginners but I'm not sure which one to choose to tune my guitar so its in synch with the course.

Note: In auto mode, when I play, a note is shown, A to G, sometimes combined with a # and with a number besides it 1 to 5. I don't really undertsand the numbers, it doesn't seem to be related to a fret.


Also one quick question:

In "Theory bascis for guitar", a graphic is shown with all the notes on the fret board. For tuning purposes, which notes should I play? Any suggestions.

Sorry if I seem a bit lost but its a lot of theory at once and I really don't understand how the chromatic tuner works. Their guide only explains the functions like "choose Key" or "input note", not really how to tune a guitar with it.

Thanks in advance for the help!