Basic nursing interventions like bed changes, transporting a patient from the bed to the chair, foley insertion, IV insertion, IVPB and maintenance, etc. Your instructor should tell you what will be expected for the check off that would include the critical steps for passing and the correct (or should I say evidence based) way of performing the procedure.
It's where you demonstrate the skills you have been taught (bed baths, changing the bed with pt in it, catheters etc...). At my school, you get a check list of the exact steps you will be tested on so there are no surprises. It's really not that big of a deal. Good luck with everything!
They are basically a return demonstration of what you have learned. There is a checklist that your instructor will be using, so just follow the steps. We had skills check offs for practically every nursing class. You will start out with some more basic skills before moving on to more advanced skills.
In my fundamentals classes, I remember being checked off on taking vital signs, doing a sterile/non-sterile dressing change, injection administration (SQ & IM, we weren't tested on intradermal but had practice in the lab), bed baths/bed changes/ROM/patient transfers. I had a separate physical assessment class so we had a check off on each body system and then a comprehensive head-to-toe assessment check off.