Where to begin...
In my opinion, there are two types of new agents: 1. Those who do it part time and work their current job full time until they replace enough of their income consistently to quit their "day job", and 2. Those who quit their full time job cold turkey and go full on into real estate. Pros and cons to both.
With all love and respect, part time agents are what gives our profession a bad name and why low cost fee based brokerages are getting traction with things like "why pay 6% to sell your home when you can have our guy push paper for $1,500?". Part timers aren't in the game enough to know when the market is shifting, they haven't seen enough to know how to deal with issues, they don't understand all the forms, etc etc. So the goal should be to get full time as fast as possible by dedicating their evenings and weekends to their skills and prospecting. Kind of like having a full time job while doing full time college.
That means you really have to decide if you're passionate enough about real estate to make it an actual job, or if you'll just keep it a hobby. It's fine if you keep it a hobby, but frankly, it's a disservice to clients to have the JV team representing them. So for hobby agents, it's best that they just do deals for themselves and keep tabs on the market. That being said, you can be a good part time agent if you are still doing enough deals that you're equal to an average full timer, or if you're keeping yourself constantly educated so you don't sound like an amateur.
As to picking a brokerage they come in two major types: full service and transaction fee based. Usually you get more with a full service but obviously pay more. Transaction fee based are good for part timers who just do the one off deal or for high motivated full timers who like to do things their way. Full service usually holds your hand through the process of becoming a pro. A shop like Keller Williams prefers you quit cold turkey, go full time, and utilize the heck out of their training and tools to get going as fast as possible. My brokerage, which is also full service but is built around property management so we don't have quite the systems KW has, tends to work well for part timers who still treat it like a job and try to get trained up as quickly as is reasonable.
With full service brokerages they come in a few types, one is large commission splits (like you get 50% to 80% of the commission) and the other is desk fees (you pay $1,000/mo to be there but keep nearly all your commission). I'm a fan of Keller Williams and some of the C21 franchisees for the full splits, Remax for the desk fee, and then RealtyPath, Equity, or Presidio for the transaction fee (there are a lot of the Tx fee popping up so who knows on that). And if you want to get into property management or investment property, then obviously I think Vision Real Estate is pretty great.
There's a lot more to this but hopefully that gets you started.