Here is some example animations you can use.

To sit on the ground, you need to play 2 animations, i.e. actual sitting on the ground, and then looping idle animation. When getting up you need to play getting up animation and normal idle animation. I.e. following animations can be used.

Sitting down

animation,,sitgrounddown,0.5;animation,,sitgroundidle,1.0,1

and getting up

animation,,sitgroundup,0.5;animation,,idle,1.0,1

To do skill roll for example searching something you can use following thing.

animation,,kneeldown,0.5;animation,,kneeldownidle,1.0,1;speak,*examining body*;speak,Examining body,4;skill,search

This will do kneeldown animation, and stay down. Then it will tell the friends that you are examining the body, and then it will tell it to dm, and finally it will do search skill roll.