Chun-Li is famously known as the first selectable female character in fighting games.
Her moveset from back then has undergone several nips and tucks over the years but the basics remain the same. As long as you can set the pace of the match of the match with fireballs, you can then use her speed to dance around your opponent.
She's one of the tougher characters in the game to master, so be prepared to rack up some losses while figuring her out.
Hyakurestu-kyaku (mash K)
Her lightning legs move. Good for chip damage but not much else, the EX version is what you want to be landing. You can combo into another EX lightning legs from midscreen, or into Ultra or EX Spinning Bird Kick when in the corner. It also rips through anyone trying to do a Focus Attack.
Kikoken (charge back, towards + P)
Chun-Li's fireball. It doesn't travel full screen but can tempt opponents into jumping, which means you can use Chun-Li's awesome jumping HP to meet them in the air. The EX version travels faster and hits twice.
Hazanshu (half-circle back + K)
A flipkick that hits overhead, so it has to be blocked high. It's a decent move because it can surprise opponents on the ground (who tend to block low when it doubt) and even if blocked, Chun-Li is safe. However, it won't beat any Focus Attacks, so be wary of opponents who like to use them a lot. The EX version knocks down.
Spinning Bird Kick (charge down, up + K)
The regular version isn't great, as it doesn't put Chun-Li in a good position once it's done. However, the EX version is one of Chun-Li's best moves. It's brilliant as a defensive option when getting off the ground, as it'll beat almost all your opponent's attacks.
Senretsukyaku (charge back, towards, back, towards + K)
A flurry of kicks that combos off pretty much all of Chun-Li's moves. However, it's better to save the meter for EX Lightning Legs or EX Spinning Bird Kick.
Hokyokusen (charge back, towards, back, towards + KKK)
A more powerful and dramatic version of her normal super. It goes through fireballs, works as a reversal against lots of moves when blocked (Dhalsim's Yoga Flame, Honda's Sumo Headbutt, etc) and combos on the end of a lot of Chun's moves (EX Lightning Legs, air-to-air HP, her Basic Combo listed below). Never throw it out randomly, as she takes forever to recover when blocked and it does almost no chip damage.
Basic Combo: back + MK > MK > down, up + MK
Advanced Combo: Air-to-air HP > HP > Ultra