Missing recovery/restore section

Hello hoping someone can help.

Imac 21.5 late 2013 (not used in a while)

A while ago i install windows 10 via bootcamp and eventually decided to get rid of it the same way. Problem is my imac has slowed down alot. Not to bad when it gets up and runnings takes ages to boot up. So i decided to reinstall osx using the recovery funtion, but the system can't find it. i think i might have done something wrong (this my first mac) when i got rid of windows.

Does anyone know is i can and where do a complete fresh reinstall in the same why you would on a new build windows pc

ps i have a separate mac disc drive if that helps

Thank you