It can look a little different depending a lot on the hen's reaction and some on the individual rooster, but what usually happens when chickens mate is that the rooster lowers a wing to signal his intentions. This is called dancing.
The hen squats. This allows her to spread his weight into the ground. If she tried to stand up, she might hurt her legs, but her squatting to spread the load into the ground allows a large rooster to fertilize a small hen without hurting her. A really big rooster on a small hen can still cause problems, but not always.
The roooster grabs her by the back of the head and climbs on. Him grabbing her by the back of the neck is her signal to move her tail out of the way. It helps him hold on and balance too, but she has to move her tail out of the way for the mating to be successful.
The rooster very quickly touches her vent with his. Sometimes it is so quick you barely see it. The rooster then hops off.
The hen then stands up, fluffs up her feathers, and shakes. She is not telling him disdainfully how little his performance meant to her. She is doing the fluffy shake to get his sperm in the correct location.
Some roosters are brutes. They don't dance and they are rough on a hen. Usually this is an adolescent and he grows out of this overactive hormone stage, but some never outgrow it.
Often a hen will resist, at least initially. The rooster has a strong instinct to make sure the eggs are fertile and will sometimes not take no for an answer. Here are some things I have observed when the hen resists after the rooster dances.
The hen runs away. The rooster ignores her.
The hen runs away. The rooster chases her. She quickly squats and everything goes as normal. She was only seeing if he was serious and really cared.
The hen runs away. The rooster chases her and catches her, often grabbing her by the back with his beak until he can climb on. Once he has a grip on her, she cooperates.
The hen runs away. The rooster chases her but quits before he catches her.
The hen runs away. The rooster catches her, she never cooperates, and he forces her.
How the hen reacts has a lot ot do with how violent the mating is. As I said, some roosters are just brutes, but a whole lot of times, roosters have been considered brutes and died more because of the actions of the hens that his actions. If the hen has the maturity and instincts to react as nature intended, the rooster would not be that rough.