Well, there are 4 main ways:

- Select your keys in the graph editor/timeline or dope sheet, and make it a clip in TRAX.
In Trax, you can do ease-in and ease-out kind of stuff.

- Select your animated object(s), open the graph editor, right-click in it there, and choose VIEW-FRAME ALL, then select a key and you will see that each key has "handles" that appear when you select them.
These "tangent" handles allow you to do many, many things.
So many in fact, that I'm suggesting you check the docs regarding all the inner-workings of using the graph editor, and working with the keyframes/tangents inside them

- Select your animated object, and in the timeline at the bottom, red lines will appear where you set keyframes.
Select them, and move them to the right to slow down an animation, move them to the left to speed it up
*Check the docs for LOTS more info regarding that as well because you are messing with keyed channels doing it that way, as opposed to the dope sheet or graph editor that let you mess with individual keyable attributes for an object

and lastly,

- Check the docs for "Path Animation".

Lots of ways to control speed in there too.

Good luck!