How does one pray sitting, and must he prostrate on something in his hand, and is it permissible for him to stand and sit on a chair only during prostration and tashahhud?

Standing, bowing, and prostrating are pillars of prayer that may not be omitted except in cases of incapacity. Whoever is able to perform some of them should do so and gesture for what they are unable to perform. If one is able to stand but unable to bow and prostrate, they must stand and gesture for bowing and prostrating, making their gesture for prostration lower than for bowing. They are not required to place anything to prostrate upon, due to the Prophet's (peace be upon him) saying: "Pray on the ground if you can, otherwise gesture, and make your prostration lower than your bowing."