Reselling bandwidth can take a lot of different routes (pun!). It essentially amounts to getting bandwidth commitments directly with the vendors and then selling off portions of that commitment to end users.
Option 1, direct ports:
So, for example, let's say you want to resell bandwidth for a banwidth company called Layer4. You'd go to Layer4 directly and you'd get a commitment of, say 6 gbps at $0.25/meg. By committing to that quantity of bandwidth, you'll achieve prices lower than smaller commitments of, for example, 1-2gbps. Additionally, you'll also get access to one or more 10gigE port(s) that you probably couldn't have gotten had you only signed a smaller commit. (Many bandwidth vendors limit your burstability/port speed to a ratio based on the commitment size.)
At this point, you have a product that smaller hosting companies can't get both in terms of pricing and port capacity. Now you just have to sell it.
In that contract you'd be allowed X number of ports, perhaps 3 total 10gigE ports...it would be however many you negotiated and would most likely be directly related to your price. You'd then approach hosting companies and see if they need ports added to their bandwidth blends. As a reseller, you'd quote them more than you're paying for it but less than they could get it on their own. You'd need to ensure your bandwidth vendor can light the building your customer is in.
Option 2, cross connects from your router:
If you're capable of operating nice routing equipment you can colocate that equipment in major telco hubs. You can then sell off switch ports to others in the building or suite.
This option is typical in situations where your customers are committing to smaller amounts of bandwidth (less than 1gbps.)
With either option:
As a reseller, you'll want to provide some kind of value beyond just price. Bandwidth prices are now low enough that many end-users actually want quality 24/7 support and will pay more for bandwidth to go direct, knowing that they can contact someone who can actually do something in tickets. Your ticket staff would likely just be passing information on to your bandwidth vendors.