Motorcycle Training / Licencing

I have been on and off bikes for a while now.

Lots of experience on a bicycle.

Motorbikes on ly in THailand:

A couple of months on a 100cc

A couple more months on a 125cc

3 more months on a 125 with a clutch.

Then tried a 200 cc Phantom: it was fantastic! I loved it. I couldn't believe the difference.

Then many months on a 125.

A few more times on a 200 cc phantom.

Then a bit on a 400cc and then a couple of times on a 600cc.

All in thailand.

What is a good website for learning how to ride / theory?

And what about test centres in chiang mai?