Users

Hi everyone… Sorry for bad English and mayby wrong category…
I use wordpress about month and I can`t find out what can I do with users.
When new user is registered he comes to /wp-admin/ and there he see information about website, he can edit his profile and so on. But I need registration only for comments. How can I shutdown “dashboard” funkcion. I need plugin or something like that? Cant understand. Or maby I need to make users categories like "members" and so on... Whell I dont know what to do so i`m asking for help. Thanks for answeres.