Of the two red arrows its the one on the right you use to fill up with oil,pop the plastic cover off then unscre it,it saves alot of oily mess if you use a small funnel when filling with oil!
There is a plug that you unscrew on the gearbox near where the rear engine mount is,take it out and pour oil into the box until oil JUST begins to dribble out of the hole,put the plug back in and thats it.
And yes,get yourself a 'haynes manual' its all in there.
Try and get a second hand old version of a haynes manual.
The old ones have a section on how to strip a gearbox whereas the new ones just say replace it.
They also have a section in colour on how to do small bodywork spray repairs.
Look on ebay.