There are various ways of training for a triathlon, but having some sort of plan to work to is going to help you get the best results.

Work back from your race date

The first thing you should do is work out how much time you have until your race day. So get a calendar, look at when your race is, and then count back from that date.
You need to give yourself enough time to get fit enough to do an event, and this is the best way to do it.

Different types of training

There are different elements to training, and depending on your starting point, you need to be sure you are covering the right ground.

Base training

This is the phase when you will improve your endurance by gradually increasing the amount of exercise you are doing. Complete beginners should be doing at least three months of this.

Build phase

This is the point when you start to increase your speed and skill level in each event for the race.

Race phase

You will usually try out some race distances within the last couple of months prior to your race to see how you get on.

Taper

You have to give your body some time to recover before you actually race, and that can be anything from one to two weeks depending on how long your race is. Ironman will have a longer taper than a sprint distance, for example, as you are going to put more pressure on your body in the race.