Bugzilla has a "voting" feature. Each product allows users to have a certain number of votes. (Some products may not allow any, which means you can't vote on things in that product at all.) With your vote, you indicate which bugs you think are the most important to be fixed.
Depending on how the administrator has configured the relevant product, you may be able to vote for the same bug more than one time. But remember, you only have so many votes to use in total! So, you can either vote a little for many bugs, or vote a lot for a few bugs.
To look at votes:
To vote for a bug:
You will automatically get email notifying you of any changes that occur on bugs you vote for.
You may review your votes at any time by clicking on the "My Votes" link in the page footer.