sale is a noun, sell is a verb you sell something (or make a sale)

sale = noun sell = verb

Also be aware of difference between "for sale" and "on sale". In the USA, "for sale" means "available for purchase" while "on sale" means "available for purchase at a discount (e.g. 50% off)". In the UK, "on sale" simply means "available for purchase".

There's a sale in the store. They are selling at 20% discount. This is how you use these words.