Sell is a verb and sale is a noun:

I'm going to sell my car and buy a new one.

She's selling bottles of water at the football game.

Yesterday I sold all of my old college textbooks on the internet.

The bookstore is having a Christmas sale - everything is 20% off.

(20% off = 20% discount)

The sales of our new product are slowly increasing.

This watch is normally $100, but it's on sale for $70.

(on sale = there is a discount)

There's also a pronunciation difference between sale and sell.

Rules to play Equestrianism

Responsibilities of governing bodies

The governing bodies of equestrian sport not only formulate the rules, but also qualify and license the officials, approve the dates and programs of the major competitions, and often act as the final level of judicial authority. They must make every effort to ensure that their rules are fair, based firmly on reality and applied accurately and consistently by officials of demonstrated competence and impartiality. They must also do everything they can to enhance and promote the quality of the disciplines and their attractiveness for spectators and competitors alike through a proactive use of their executive powers. Finally, they must recognise that neglect or disregard of the ideals of fair play reflects both on the sport and on the organisations responsible for its conduct.