What is the meaning of taslim here:

'The Night Prayer consists of eight units of prayer; each two alone. Taslim should be said at the end of each two units with the intention of offering the Night Prayer.'

Taslim means giving Salam at the end of each two units. As you know that all Mustahab prayers are of TWO Rak’at (units) only therefore after every 2nd Rak’at one should say both Tashahhud and Salam then stand up for Next salat and he/she not allowed to connect each of them. So it’s simple after second Rak’at we should say Tashahhud and Salam and finish our namaz of two units then stand for next salat.