Hello rrannala, basically, route shopping is when you you schedule a lot of shops along a particular "route." Many shoppers will find a high-paying shop somewhere as an "anchor shop", i.e. a shop that's worth making a long drive. Then they will find other shops in that area and along the route to supplement their income and offset expenses. A route could be anything from a single day trip to multi-week excursions. Route shopping allows you to do shops whose fees are not worth the drive by themselves.
For example, there might be 100 gas station shops in your state. You plan a driving route that let's you get as many done for the least cost and drive time. Then you look for other shops along your route. Typically, you find shops through many MSC's.
Some shoppers have negotiated higher fees for their routes due to being willing to complete a lot of shops and being able to get those in out-of-the-way locations. Of course, having positive history with an MSC helps when negotiating bonuses. As for what MSC's offer routes, that really depends on where you are. You can build routes with whatever shops are available. Sign up for as many MSC's as you can and see what's available near you.
A piece of advice: don't overbook yourself. While you might be able to complete 20 shops on paper and under ideal conditions, you might be better off with smaller, shorter routes as traffic, weather, and chatty salespeople can easily turn your plans sideways.