i want to get into gundam where do i start? ive heard very good things about Witch from Mercury and Iron Blooded Orphans
the short answer is: start at whatever gundam series you think looks the coolest, go from there. i recommend gwitch/witch from mercury, but anything works tbh
the longer answer is a little more complicated, but effectively means the same thing. stuff like gwitch (witch from mercury) and IBO are known as gundam AUs, so you can honestly just hop in with either of those. gundam AUs are their own stories, they have no relation with other stories outside of having gundams/mobile suits and some generally similar themes and story beats, but ultimately they're their own thing.
universal century (or UC) is the "main" gundam timeline (aka the central one), which starts at the main mobile suit gundam, but the AUs like gwitch and IBO are separate
so really, you can just start with an AU, and go from there. that's what i did - i started with an AU (gundam thunderbolt), i watched the original series (the movie trilogy, anyway), and then i went to G gundam (an AU), and from there i was hooked
in my opinion, gwitch is a fantastic place to start for gundam, since a lot of people i know have enjoyed it, and it's relatively short and easy to digest at 24 episodes. IBO i've heard good things about too, but that one is very much a "you'll like it or you'll hate it" kind of show. if you think it looks interesting, go for it! really, you can just kinda browse around gundam stuff and if you go "woah that show looks cool", i say start there