There are four Mandatory things (Farz) in Wuzu.
- Wash face one time.
- Wash hands till elbow one time.
- do masah of one-forth of head one time
- wash feet with ankle one time.
(Surah Ma'idah - Ayah 6)
O you who have believed, when you rise to [perform] prayer, wash your faces and your forearms to the elbows and wipe over your heads and wash your feet to the ankles. And if you are in a state of janabah, then purify yourselves. But if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and do not find water, then seek clean earth and wipe over your faces and hands with it. Allah does not intend to make difficulty for you, but He intends to purify you and complete His favor upon you that you may be grateful.
The Messenger of Allah performed ablution washing each part once. He said: 'This is the ablution of the person from whom Allah will not accept his prayer without it.' Then he performed ablution washing each part twice, and he said: 'This is the ablution that Allah appreciates.' Then he performed ablution washing each part three times, and said: 'This is how ablution is performed properly, and this is my ablution and the ablution of the Close Friend of Allah, Ibrahim. Whoever performs ablution like this, then on completing it says: 'Ashhadu an la ilaha illallah, wa ashhadu anna Muhammadan 'abduhu wa rasuluhu' (I bear witness that none has the right to be worshipped but Allah, and I bear witness that Muhammed is His servant and His Messenger), eight gates of Paradise will be opened to him and he may enter through whichever one he wants.'"
Apart from mandatory(Farz), others thing are Sunnah.. If you only Follow the Farz of Wuzu, it is ok, you can perform Namaz. But to gain more Sawab, it is highly recommended to follow Sunnah way of Wuzu and follow its Mustahabat and avoid things that are prohibited.
You can find more about Sunnah, Mustahabat and Prohibition for Wuzu here