there are a couple of clubs around that do agility training.
for some info on clubs & agility in detail- try this website

I saw some agility tools they use in competitions (tunnels, weave poles, jumps..etc.) for sale at Target. If you train them with these kind of things it should help.

Your best beginning would be to join a local club. If you post your county, I can help you find one.
Here is a site to help you set up your own course>
this site has helpful links>

If you are in UK I think that you will find that your Pitbull cross is banned!

Look on the net to see how some courses are set up. Run through the course and have the dogs follow you. If you act excited about it and are having fun they will do the same. When they are done with the course give them a lot of excited attention and praise and a small treat.

Someone experiences in training would help the most, but at Target this weekend I saw that they now sell a whole line of agility course products. They have a training book and all the props for sale. You could check there for an informal start.

Find a training center that will teach you the basics. There are several places in a 20 mile or so radius around my part of New England.

I recommend calling your vet or other friends that do agility training and taking your pets to a licensed agility trainer. They can help you learn how to train your own dogs and help you learn how to set up an agility course in your backyard.

You can start by joining your local agility club.

If this is your first time training agility, you are best to find an experienced trainer in your area and take classes.