بسم الله الرحمن الرحيم
Four categories of prayer
There are four categories of prayer: fard, wajib, sunnah, and nafl. Each category has a certain priority and importance.
Below is the table that shows what categories we pray for each of the five daily prayers, and how many rakaat is each prayer.
Table of prayer categories and rakaat*
Colors show the category, and digits show the number of rakaat in each prayer.
* Rak'ah (pl. rakaat) is a basic prayer unit consisting of standing, bowing, prostrating, and sitting together with Quranic recitation and dua.
Fard - essential: they are the five essential daily prayers. An absolute must for every sane Muslim who reached puberty. Friday prayer is also a fard for men. Praying fard prayers has the greatest reward, and not praying them is a grave sin.
Wajib - obligatory: wajib prayers are obligatory, but a level below fard. It is a category specific to the Hanafi school of law, while the other three schools consider these prayers to be sunnah. A prominent example of such prayer is Witr, prayed after 'Isha. It is the most important prayer to establish after the fard. The two Eid prayers are another example.
Sunnah - emphasized and non-emphasized: these are the recommended prayers that were performed regularly by the Prophet Muhammad (peace and blessing be upon him). They are of two categories: emphasized (muakkadah) and non-emphasized (ghayr muakkadah), while the most important among them is the sunnah of Fajr.
The emphasized sunnahs should eventually become a part of your daily practice on top of obligatory prayers. Habitually leaving the emphasized sunnahs is blameworthy.
Nafl - optional: nafl prayer are optional prayers that can be prayed almost at any time, and praying them is rewarded. However, not praying them is not sinful. They are indeed optional, and go on top of all the other prayer categories.
A recommendation for beginners
Some prayers are more important than others, so we adopt them in the order of priority. This categorization brings a great ease to beginners, and gives us the understanding that all good actions in life have certain priority, and we start from the most important ones.
Thus, a beginner should start from the fard prayers, and make them an integral part of his life. Together with the fard, we strongly recommend to pray the sunnah of Fajr and the Witr prayed after 'Isha. If that's too overwhelming, at least establish the fard. Once the fard is established, add other prayers in the order of importance. Assess your strength correctly, and proceed with firmness.
May Allah give us the wisdom to see the priorities of things and grant us the success to act in accordance with that wisdom. Ameen!