To see a list of a user's contributions, go to their user page or user talk page. When you do that, the menu item "User contributions" will appear in the Toolbox menu on the sidebar. This link will show you all the edits that user has ever made (except deleted edits), up to 500 per page. This is useful for tracking vandalism in progress.
Edits with a "top" link are the most recent ones to their respective articles.
You have your own contributions list, which is particularly useful for tracking your conversations on talk pages. If you are logged in, you can access the list from the "Contributions" link at the top of the page.
To help keep track of your discussions on talk pages, you may wish to place the {{Discussion tracker}} template to your talk page.
