sister,
Night prayer(Qiyam-al-layl) is similar to any other prayer except it is prayed in the night after Isha and before Fajr time.
You can perform many 2 rakats as long as you wish and finally when you decide to end you have to finish with one rakat. This is because Allah likes witr(odd) number.Qiyam-al-Layl is known with different names like Taraweeh(performed in Ramadan first part of the night), Tahajjud(performed in 3rd part of the night) and witr(odd paryer, this name is commonly used in indian subcontinent). Many people think it is part of Isha prayer but in reality it is not. According to many madhabs it is sunnah but according to Abu Hanifa(r.a) it is wajib to perform witr prayer.
If you dont have time or got tired, atleast you can perform one rakat and finish the prayer. Last days of Ramadan are very important and blessed days. So it is best to perform as many rakats as possible.
I recently saw the big article in TTI abt qayam-al-layl, you can search and read the entire information.