Hey guys ive been playing around with the 4 track we have got and i understand everything on it except an input (or is it an output??) which looks like you plug a guitar in it.
It's called a punch inout and i have no idea what it does.

I've looked around the site and it seems noone has really mentioned it, also i "googled it" and i had no friggin idea what people there are talking about.

So sorry if i missed it somewhere along the line of someone already posting it but could someone please tell me what it is and what it does?

The following is a piece of a manual from Sagan technology. The basic is that you can plug a switch pedal into this jack and do the Punch In/out recording

Punch Recording

Recording only within a particular range of a track without altering recorded data before or after that range is called 'punch' recording. Punch recording allows you to re-record specific areas of a track without altering the entire track.

Metro allows two punch record methods: Overdub and Replace. Replace replaces existing data in the punch range with what you subsequently record. Overdub retains all existing material, placing what you subsequently record on top of previous material in the punch range.

You can specify a punch range either by graphically selecting it or by entering the Punch In and Out times directly in the Punch In/Out dialog box (available by clicking the door of the Punch setting in the lower right part of the Transport window). If your punch range is not very long, you may prefer specifying it graphically. You can set a punch range of any length at any point in the track.

To punch record a track:

Record enable the desired track in the Tracks window by clicking in the 'R' column, placing a dot there.

Do either of the following:

Set a punch range in the Graphic Editor window by:

a) Opening the Graphic Editor window for the appropriate track and choosing the Arrow Tool

b) Clicking the Bar Number in the Time Line where you want the punch range to begin

c) Dragging across the desired punch range and releasing the mouse after selecting the end point of the punch range

Set a punch range in the Punch In/Out dialog box by:

a) Clicking the door in the lower right of the Transport's Punch setting to open the Punch In/Out dialog box

b) Typing the In and Out times in the Bar, Beat, Clock fields

c) Checking the Stop playing at punch out time box if you want playback to stop at the Punch Out time, rather than continuing until the end of the track

d) Choosing a Record mode by clicking either the Replace or Overdub button and clicking OK

Notice that the Punch setting in the Transport is now highlighted, which indicates that Punch Recording is enabled.

Click Record or press Option-R.

Play your controller to record some music.

Metro stops recording when the counter reaches the punch out point.

Listen to the track again. If you don't like the new recording, choose Undo from the Edit menu and repeat steps 3-4.

Another description of punching:

The technique of inserting a signal into an audio track.  Placing the recorder in and out of record at specific locations in the track.
Punch-in is a useful technique for correcting performer mistakes or inserting material into already recorded tracks.
 

 
Have the player monitor the pre-recorded material on headphones to avoid track leakage.  Playback the recorded material some distance before the punch in point.  At the appropriate place in the track punch in the record button on the recorder for the player to record the new material.  Punch out of record as soon as the player has finished the new material or when the previous part needs to be back in. 

 
This takes practice! 
Some recorders provide a rehearsal mode which mutes the track to be recorded but does not actually record anything so both the engineer and player can practice their moves. 

OK? Now do your job!