Down at the bottom of the page, there are a couple of links - Ðåãèñòðàöèÿ   (registration) and Âîéòè   (log-in)

Registration is pretty simple, just give a username, full name, and email.. and it will mail you a password. Other fields are optional. Here's a translation of the form:

Once you have registered and logged in, you will notice your User-Name appears near the top right of the page.
Also, any thread ("Tema" in Russian!) that you click on will have a little form at the bottom, so you can add a reply if you wish.

Other links at the bottom of the page:
( Âîéòè      |      Ðåãèñòðàöèÿ      |      Ïðîôàéë      |      Ïîèñê      |      )

Ïðîôàéë  is a link for you to edit your profile.

Ïîèñê  is a link to Search the forum. 

PLEASE NOTE: the two buttons for submitting a posting are "Ïîñëàòü" (submit) and "Î÷èñòèòü ïîëÿ" (reset form!)
"Î÷èñòèòü ïîëÿ" will NUKE everything you just typed, so try not to hit it by mistake!