Confused about reinstall

Computer engineer had to install new hard drive yesterday. Returned laptop to me today and said uninstalled Windows 10 and had to install Windows 7 and I would get lots of updates.  Put on another brand of internet security (not sure who's) but I said I was half way through 2-year cover with AVG Internet Security but also have 1-year's worth taken out this November for AVG TuneUp.  Don't understand how to reinstall either but can't afford pay someone to do it for me.