The period where you were a new member was the “novitiate”, so newcomers were novices, just like in any other monastic order. The Templars were, technically monks first and foremost, although in practise their duties as warriors ended up being more important than monastic duties.

If you wanted to join the Templars, you would first have to show that you were really committed. The commander of the local chapter that you wanted to join would question your sincerity, then send you away to think about it. If you came back you would be questioned again, and sent away again. If you came back a third time, you would have to swear a solemn oath that you were sincere.

At first there was a one-year probationary period, after which novitiates could officially join, but that seems to be an early rule that was later abandoned or ignored. By the time the Templars were suppressed in the 14th century, there was no longer a probationary period. You became a full member as soon as you joined. At least for the Templars in the crusader states in the east, this is probably because of the military circumstances, where they lost a lot of members in battle and needed to replenish the ranks quickly.

It was made clear to prospective Templars that, even if it looked like the order was rich and powerful, it was actually a life of hardship. You took vows of poverty and chastity, and whether you were a powerful lord or a lowly soldier, every new Templar was supposed to have the same low status (although of course it didn’t always work out that way in practise). You could be told what to do, where to go, when to fight, when to eat, when to sleep - everything was rigidly structured.

Some monastic orders allowed children to join as “oblates” (i.e., people who were “offered”, sent there by their parents for example), but that practise was already rare when the Templars were founded in the 12th century. Children could be committed to the order but they wouldn’t be allowed to join until they were old enough to fight, so they would have to be teenagers at least. Older men with plenty of experience in battle also joined - you could be a widower who preferred to join the order rather than remarry, or there are some famous examples of men joining on their deathbed simply so they could say they died as a Templar. You might also join along with your wife - although women weren’t allowed to be Templars so she would become a nun in a regular monastic house.

As a warrior knight, you’d spend a lot of your day training for war, especially if you were young and inexperienced. But as a monk, you were also supposed to learn various prayers and spend a large part of your day praying. That wasn’t really practical for knights and sergeants, so there were Templars who were strictly “religious” (i.e. more like regular monks) who would perform all the prayers and services for the “lay” brothers. But new knights and sergeants were expected to recite certain prayers (including 18 Pater Nosters per day).

We don’t really have any information about what life was like for a novice knight - did they have to eat separately? Did they have their own sleeping quarters? Did they eat different food, wear different clothes? There seems to have been no differences between novices and other members, especially when they got rid of the probationary period. But there were sergeants as well, foot soldiers and assistants who weren’t knights, and they probably did all the menial jobs. A new sergeant:

“may be told to carry out one of the basest tasks that we have, perhaps at the oven, or the mill, or in the kitchen, or with the camels, or in the pigsty or several other duties that we have.” (Rule of the Templars, ch. 662)

The actual initiation ceremony became rather controversial when the order was suppressed and the Templars were put on trial in the 14th century. Some Templars claimed their initiation included homosexual acts and Satan worship. It’s likely that the inquisitors already had these charges in mind and then tortured the witnesses until they agreed - there is no other evidence that the ceremony was ever really conducted like that.

I should also note that the suppression of the order occurred in 1312 so there is no “legit” Knights Templar order. There are several groups that claim to be modern continuations but no matter what they say, none of them have any connection whatsoever with the original Templars. I’m not sure where you are, but I’d be rather suspicious about anyone claiming to be a Templar these days…but I suppose that’s a different question entirely and probably violates the 20-year rule…

Sources:

Malcolm Barber, The New Knighthood: A History of the Order of the Temple (Cambridge University Press, 1995)

Malcolm Barber and Keith Bate, The Templars: Selected Sources (Manchester University Press, 2007)

Judith Mary Upton-Ward, The Rule of the Templars (Boydell, 1997)

A.J. Forey, “Novitiate and instruction in the Military Orders during the twelfth and thirteenth centuries”, in Speculum 61 (1986)