Let me present you with a hypothetical situation.
Imagine you haven’t played a role-playing game in months beyond the occasional one-shot session. You decide to fix this travesty, inviting a handful of close friends over one night so you can kick down some dungeon doors and kill some pesky monsters. The typical activities of an adventurer.
Eventually, your friends arrive to roll some dice and have some fun. Everyone takes their seats around the dining room table, and you as the Game Master have to make a quick decision. You could jump into this new campaign head first, or you could spend this session preparing with your new group to ensure the health of said campaign.
I suggest you choose the latter, having yourself a Session Zero.
Session Zero is like a prologue for a campaign, the session before the actual campaign that allows you to lay down a solid foundation to ensure it goes off with as few hitches as possible. You can make sure everyone is on a similar wavelength on what kind of campaign they want to play, work out any compromises that need to be made, create characters together that will not step on each other’s toes, and possibly even figure out a reason for said characters to be adventuring together in the first place.
I know it might seem strange to not have the first session of a campaign be one where you actually play it, but I staunchly believe a campaign that is kicked off with a Session Zero will be of higher quality than one that just dives in.
Just give it a try. I promise you won’t regret it.