To log in, simply select your name and type your password in its field, then click "Login"
Once logged in, you will be redirected to another page in which you can browse law proposals being voted. To vote, simply click "Yes", "No", or "Abstained" at the right side of the table in the row corresponding to the proposal you want to vote
To log out, click the "Logout" button at the top of the page just below the title