Question 2d Skeletal Animation body and arm/item separation

Hello,

I apologize in advance if this is a simple question I am just having trouble knowing keywords/terms on what to search in order to better research.

I recently started using the skeletal rigging and animation using the PSD importer and its been great. But my question is the best practice/way to animate two parts separately?

For example the Unity tutorial shows a character in an idle position with a weapon and creates animations based off that.

How would you go about using animations for movement(idle, walk, run, etc) as well as being able to swap weapons when the arm positions would change (ex: pistol position, rifle position).

I guess I am just confused on what to search in able toto research more into the topic where you want parts of a skeleton (arms in my case) in certain positions based on an item and rotatable and how to separate that from the rest of the body and its animations.

Sorry again if this is confusing I am having a hard time myself explaining it. But any advice and terms to research would be greatly appreciated.

Thanks again