How Do I make A Custom Animation Interaction (not tuning)

Do you mean that you want to add existing animations to your object? Are you referring to animations with the object itself, or animations between a sim and the object?

The later is, in fact, described in the object's tuning. Each object has specific super affordances, described in its tuning file, that dictate which type of interactions (with adjoining animations) are available with that object. You can add interactions to your object by adding different super affordances. However, if you, say, created a couch and cloned it from an existing EA couch, it will automatically inherit all the same super affordances EA couches have because each custom mesh automatically inherits the tuning of the object it is cloned from (unless changed in studio). You can also create custom interactions and use existing animations to go with those interactions but this is a far more time consuming process that requires knowledge of the game's xml.

Animations with the object itself are far more difficult, for they require custom animations as well as a lot of new coding and so far very few people have succeeded in successfully doing this (it is also very time consuming and requires knowledge of the game's files because there is no tutorial available).