There is a great article on succession sowing/second cropping on this site by Charles.
If you type “succession” into the search box it will bring you to it.
Rotation is a simple concept to understand.
Broadly speaking plants are divided up into different plant families.
Being simplistic, our veg is divided into 5 families; Potatoes, Legumes (eg Peas/Beans), Brassicas (eg Cabbage, Cauliflower), Onion (eg Onion, Garlic, Shallots), Roots (eg Carrots, Parsnips).
Each of these are vulnerable to specific pests and diseases. To avoid a build up of these pests/diseases we plant each family in a different section of our plot every year, i.e., we rotate each family to a different bed each year.
This is a huge subject in itself and it is well worth putting a bit of time into researching it.
The basic concept is quiet simple but there are nuances which need to be understood also.
Don.