There are a multitude of training plans available for marathon training. For beginners most suggest a 16-week training programme at least, although London Marathon advise a 20 week programme. Ultimately it depends on your ability to run and how confident you are already. If you have never used a training plan before there may be some specific words and phrases you may not be familiar with when reading a programme:
Fartlek (Interval) session: A Swedish word literally meaning 'speed-play'. It describes a run where speed is simply varied over time. So, an easy session could be: Run steady for 3 minutes, run hard for 1 minute, repeat 5 times. These sessions mainly will help improve your speed endurance.
Progression run: A session where the aim is simply to reduce your time per mile/km of the run. For example: begin the 5km run at 6 min/km and finish the final km at 5 min/km.
Hill run: Hill running works the legs far more intensely. If you are new to hills, be prepared to tire quickly. The idea is to tackle the hills with a shorter stride, picking up the knees and driving the arms as you do so. Long term, hill training will make your runs on the flat feel far easier.
Long run: The aim of the long run is to acclimatise your body to running distance. The key is for your long runs in to be at a slow pace - you wouldn’t want to run your first 16 mile run at marathon pace!
Recovery run: This run is as it says - to recover. No PBs to be broken during this sort of run. The day previous may have been hard and intense or your long run; so here the aim is just to tick the legs over and flush out any tension.