Twelve sunnah rakat surround the obligatory prayers: 2 before Fajr, 4 before and 2 after Dhuhr, 2 after Maghrib and 2 after Isha. Whoever keeps them, a house is built for him in Paradise.
Witr is an odd-numbered prayer (at least one rakah) prayed after Isha, ideally as the last prayer of the night. The Prophet ﷺ never left it, even when travelling.
Duha (mid-morning) is the prayer of the grateful, and tahajjud in the last third of the night is the honour of the believer — when Allah descends to answer those who call on Him.