Sit back -no effort 

I sat back whole hours while he was cooking cuisine. 

Sit in on -observation with out participating

He sit in on many classes before he starts his own courses 

Sit through -stay until even it is boring 

We sat through whole lecture even it was quite easy for us,. 

Sit up-pay attention

He sat up when teacher called his name. 

Sit out -No participate 

We sit out till the game was over.