The Poll core module lets you create simple polls. You ask a question, provide possible answers, and let your users vote. Drupal then keeps a running tally of the results.
When you create a poll, Content >> Add content >> Poll (Drupal 5 and 6) or Content >> Add content >> Poll (Drupal 7), you can also specify the "base" vote counts (how many votes an item has at the start) and decide how long the voting will run.
You can enable the polls module on the modules page, Administer >> Modules.
The poll item in the navigation menu will take users to a page where they can see all of the current polls, vote on them (if they haven't already) and view the results.
On the access control page, Administer >> Access control (Drupal 5 and 6) or Modules >> Poll >> Permissions (Drupal 7), you can decide which users have permission to vote, to see the voting results, and to create polls of their own.
To change the settings for creating polls - Administer >> Settings >> Content types >> Poll >> Edit (Drupal 5 and 6) or Structure >> Content types >> Poll >> Edit (Drupal 7).