Trade - Character to Charcacter

how can I trade items from 1 of my characters to another

Send in email or open 2 client and do trade?

.... and how?

Use the mail system in game .

how to use the mail

Go see the mailbox in game and send a mail to your other character then first tab and first button on the right.
Enter the name and put your item then send it first button at the bottom.

I can't select the name of my other character

Don't select it you have to type it and that should work.

exactly, but doesn't appear

[You must be registered and logged in to see this link.] your two characters must be in different accounts to send a mail, otherwise you can't trade between them.