I use wordpress 4.0, but the new register, do not send mail activation. Please help me
my website :

[@robkk Moderator 9 years, 11 months ago]

there are tons of plugins that add this kind of feature, some with custom login and registration forms and other features too.

this plugin does just like you want.

https://wordpress.org/plugins/dm-confirm-email/

you should also do a google search for other plugins if you want to find something different.