1. Fajr – 2 Raka Sunna followed by 2 Raka Fard
2. Zuhr – 4 (2 and 2) Raka Sunna followed by 4 Raka Fard followed by 2 Raka of Sunnah
3. Asr - 4 (2 and 2) Raka Sunnah followed by 4 Raka Fard
4. Maghrib – 3 Raka of Fard followed by 2 Raka of Sunnah
5. Esha - 4 (2 and 2) Raka Sunnah followed by 4 Raka Fard followed by 2 Raka of Sunnah followed by 3 Raka of Biter.
Each of the five prayers has obligatory part called the Fard and the voluntary part called the Sunnah that used to be prayed by Prophet Muhammad SAWS, furthermore, these parts have designated numbers of sections called the Raka.
Biter is in between obligatory and voluntary, meaning there is a lot of emphasis to pray these three Raka of Biter.
So, as you can see, Islam is very structured. If you ever wondered, in a group prayer, how does everyone know to vow together, well, this is the secret, each prayer is structured, in addition to knowing the above numbers of Raka, they know the steps within a Raka. For example, each Raka has 1 vow and 2 prostrations.