Companies like Coldwell Banker, Century 21, Keller Williams, Re/Max and others are national companies with locally owned franchises which will sponsor a new agent as a Sponsoring Broker.
As a new agent, you will have the opportunity to interview and talk with potential sponsoring real estate brokerage firms to see where you fit best as an individual with your business goals. Each firm will offer slightly different benefits to joining their firm. There are both pros and cons to going with each firm. National franchise firms might offer things that local firms do not and vice versa. With the internet leveling the playing field, it is my opinion that belonging to a large national franchise is not as important as it may have once been in decades past.
In the older days, prior to the internet MLS, it was probably very beneficial to have been a part of a large, national brokerage firm where you could easily network within your office to learn about new listings on the market for your clients. This also allowed an agent to easily spread the word about their new listings in hopes to attract the buyer client of another agent in your office. That all changed with the shift to the MLS online.
Agents are no longer required to be in huge offices in order to spread the word about their new listings or to find the newest listings available for their clients. The internet allows small firms to know of listings and promote listings just the same as an office with 500+ agents. In fact, some would argue that you have more opportunities at a smaller, local firm because of the attention you will receive from the lead Broker and managers. Your clients are likely to get better attention from smaller firms as well as the corporate structures of larger firms.
However, in an effort to be fair, there are things you will get with larger firms which you will not get with smaller firms. Larger, national franchises tend to advertise their brands through both radio and television advertisements. Large national brands will also usually have marketing materials available (for a cost) to their agents where the agent will not have to take the time to design their own marketing materials. On the flip side, most smaller firms do not have readily available marketing materials and this means that the agent will have to spend time and money designing their own promotional and marketing cards, brand, etc...
In addition, most national brands are well-known and clients. Consumers will most likely know of the large national brokerage brands with no explanation needed by an agent. This could also be a double edged sword. Some potential clients may have had a prior bad experience with an agent from a national brand and, although every agent is not the same, some potential clients with prior bad experiences may hold this against you if you are part of the same brand.
As the use of the internet grows in real estate (with no signs of slowing), it would be my personal recommendation to seek and interview brokerages who seem to understand that a great internet presence is a must when moving forward in today's world. Questions to ask on this front would be - how are your organic internet rankings? How many people visit your website per day or month? Do you update your blog often? Do you allow your agents to write for your blog to grow their own personal brands? Keep these questions in mind when you interview brokerage firms.