When people say they have to CATCH a bus, or a cab (taxi) or a train, they are usually talking about a trip without a reserved seat.
For example, I might catch the bus to work every day. I get on, pay the fare and sit in an unreserved seat.
However, if I were going on a trip and had bought a ticket in advance, I would say I am TAKING the bus to Toronto.
If I live in a big city, I CATCH a cab or taxi by going out on the street and waving one down, then I tell the driver where I want to go. I would say I am TAKING a cab if I have called ahead and asked for the cab to come to my home and pick me up.
The use of CATCH is usually describing a trip that is not pre-booked.
Hope this helps