I know it looks like there's a lot but it is really easy since most shows are considered to be alternate universes with no connections to each other. There will be some shared tropes like the "Char-clone" aka the character that wears a mask but it is not necessary to know all those things. If you want to get into the main Gundam timeline then there's a certain watch other but to get you started I will focus on the AUs.

Now the big question of "Where do I start?". I'm gonna list a few of my favorites that you can watch as a beginner but it is by no means the only ones to watch.

Gundam 00 - Probably my favorite on the list. Great characters, great mecha designs, and a decent story split over two 24 episode seasons and a movie.

Witch From Mercury - The most recent entry that actually finished its story today. Has a younger cast since it has a school setting. However do not expect this to stay light hearted because of the setting.

G Gundam - A bit older since its from the 90s. Basically what if you took the action of DragonBall Z and did it with giant robots. To get the full effect you must watch the dub on this one.

Let me know if you have any questions, I'm a huge fan of Gundam and love helping people find the Gundam for them.