Leuven Volley is for all players in and around Leuven, so also for beginners who have never played before or those who last played many years ago. If a session’s name or description doesn’t exclude beginners, you can join. A standard session starts with a quite lengthy warming up, if you have questions about technique, rules, etc. it’s a good moment to ask them. During the game it’s also possible to get tips or ask simple questions but there is no time to go deep.
To be better prepared you can watch some YouTube videos about basic technique, read the rules (I found the official FIVB rules a quick read, but there are enough good summaries on the internet), and go through this basic strategy.
Whatever your preparation, most things will become clear soon enough.