When visiting the profile of another member, you can see what the member has been up to recently on the forum from the Activity tab provided on the profile page. Some of the info you'll see here will let you know what topics the member has posted recently, what threads they have created recently, any profile updates, when they liked a post on the forum, and more. These items will be listed in order from most recent to oldest. If a member has an extensive activity history, you can click the Show More link at the bottom of the feed to load more activity.
If you're viewing your own activity page in your profile, you'll have a couple of different options that you won't see when viewing the activity of other members. The first difference is the status bar toward the top of the page allowing you to update your account status directly on the activity page. The status activity you post will be listed on your activity feed. Also, if for some reason you want to remove an activity from your own activity feed, simply hover over the activity mentioned in your feed that you want to have deleted, and then click the Delete link that appears to the right of the activity.