I simply dont' understant how to modifiy (if it's possible) some parameter for register area (module?)

how can I add forms ?
how can I tell to DNN that I prefer use the email as login and not a nickname
how can I view all the option of the register module (if any)?
I saw that I can use a security code, but how I can set up this option? I don't see it
it's possible to send a link .as a securty option insted a security code, i mean.. it's a simplier way the users have only to click to complete the register process.

David