On litphoria, you can either browse the site with no character, or an active character. Many actions on the site require you to have an active character, such as making a post to a roleplay. While you have your active character set, that character's online time will update every 15 minutes or so. This bumps you up on search results, and lets friends know you're online with that character. With an active character, there's no need to select which character you want to use for an action - your active character will be chosen for you!
If you have lots of characters, don't worry. Switching characters is easy, just go to your account settings. After you have a character set as your active character, you can switch even more quickly by clicking their icon in the top right, hitting 'change character', and clicking on the picture of the character you want.