Open up Steam on your laptop/desktop and log into your account.
Go to the upper right-hand corner and click on your profile.
From the drop-down menu, select the View my profile heading.
Go down into your profile and click on the Edit Profile button.
Look at the side menu on the left-hand side of the screen. Click on the last heading on the menu, called Privacy Settings.
From the Privacy Settings page, scroll down slightly and click on the Game details heading.
From the small drop-down menu, click on the Private button to ensure that no one can see which games you are playing and when. If you want your friends to be able to see this information, then click on the Friends Only option.