Well, for people JUST starting out on emerald TR, your two options for starting out would either be 1TR or AODR.
AODR is your typical "zergfit"; they field LARGE numbers of players who may or may not be any good at the game. Their platoons are open, so anyone can join, but if they need to make space for an AODR member, then they'll boot someone without the tag. The platoons are really hit or miss. Sometimes you'll get an effective zergherder who'll take you to the fights you want to see and show you a good time, other times you'll get some boring person who'll send you to massively overpop and ghostcap some base while you just sit there waiting for the base to cap and hoping some schmuck leaves the enemy spawn room so you can kill them. It really depends on what you're looking into. If you gitgud in AODR, there's a small squad of skilled players in the outfit called the "reapers", and they're fairly capable. You could, in theory, just spend your time in AOD, moving up from a typical grunt to a squad lead and then a platoon lead, go into reapers, etc.
1TR is a midfit; they usually field 3 squads to a platoon of people, and they're standard midfit fare. They're more coordinated with each other than an AODR zerg, and a bit more capable on an individual skill level (on average) than typical AODR members. Their requirements are mainly that you have teamspeak and be not-braindead, so you could join pretty easily, and they generally have more experienced players on average, so they'd probably teach you the basics better than AODR. That, and when they run ops, they're usually more reliable (in terms of not-ghostcapping empty bases) than AODR. The main issue is that they seem really… reddit-y? You might not necessarily like them as much, and it's not like AODR where's there's just tons of people; there's an outfit culture that I'm sure some anons here just wouldn't get along with.
From there, for more experienced players, you have specialized vehicle or infantry outfits. There are tons of infantry outfits around on TR; I know J0KE's pretty good from having ran with them a couple of times, but their stat requirements can be a little uptight, and they expect a lot from each individual member. They've also been playing more NC and VS lately since TR are overpopped, though. I haven't really ran with much other infantry outfits, but I assure there's plenty of them.
The big vehicle outfits on TR, if you're into that, are ECUS, HONK, and FedX. FedX runs more with battle sunderers (the big buses that you can deploy for a spawn point), although they do all kinds of vehicles. ECUS is a harasser-focused outfit and almost only drives the harasser (the 2-3 man buggy; it goes fucking fast, is fucking fun, and is fucking deadly with people who know how to use it). HONK does lots of different armor, and I know they also dabble in air, as well.
There are probably plenty of other outfits to join, but those are the ones that come to mind first.
The TR's prowler ends up playing a lot like artillery.