I'm no animation expert, but I'll try to help with your questions.

1. There is a tool called Empties on the left toolbar that looks like a set of axes (3 lines poking away from each other). Currently it is in the second to last grouping below the lightbulb. Empties are similar to groups, but also have position information built in. You can animate an empty, but not a group. You also have to create the empty first. Here is a workflow.

a) Add your parts for your model.
b) Add an Empty to your model. Since you will be moving the Empty and its' children together, you need to place it where it makes sense. For instance, at the shoulder snap point for a minifig arm. To do this, select the snap point and then select the Empties tool. You will have an option of axes, sphere, or cube. Any of these is fine, as it won't come out in a rendered animation.
c) Now you have to get your parts into your "Empty Group." The method for this is called parenting. I will give you two options for this:
A.1) Select your parts (the arm and its hand).
A.2) Select the Set Parent button (Axis with arrow pointing in, just below the group folders in the left toolbar)
A.3) Select the Empty where you want them to go
-or-
😎 Drag the parts you want into the correct empty in the Graph tab on the right hand sidebar.

Note that in the picture above, where the Empty is placed, if I rotate it, the brick will move around like a circle. If I want it to spin, then I need to move the Empty to the center of the brick BEFORE I set the parent.

Ah! That make sense! Thank you so much!

Hey how do you make an animation for your build?

PS.

Video walkthrough would be appreciated.

try this:

https://www.mecabricks.com/en/forum/topic/3171