You can animate text on a text layer, character by character if you want. To do so, you will have to add new items to the Timeline. These items are called Animator Groups, Properties and Selectors.
Properties are the specific aspects you can animate. For instance, if you want each letter in the word cat to, in turn , grow bigger, then smaller (cat, cat, cat, cat, cat), you need to add a Scale property.
Selectors constrain your property animations to particular characters within a text later. For instance, if you want to animate the scale of only the P's in the word "hippo," you need to add a Selector that isolates them from the rest of the word (hippo).
Properties and Selectors are contained within Animator groups. To animate letters rotating, you add and Animator Group to the text later. Within the Animator Group, you'll find a default Selector, which (by default) selects all of the characters on the layer. You'll also find a default property (in this example, rotation). If you want, you can add additional Properties and Selectors to Animator Groups. You can also add more than one Animator Group to a single text later.