Configuration of IAX between 2 Asterisks

I try to connect 2 Asterisk. The first one can manage two phones connected to a SIPURA SPA 2100 and the second one can manage txo phones connected to a TELCO GW-232.
I want create a trunk between my first Asterisk and the second one. I thnink about IAX in order to connect my Asterisks but I don’t understand this protocol.
Do you have explanation or configuration about iax.conf.