Suppose you were to visit a certain place, and you had no idea as to what that place is like and you were too lazy to do all the research for your visit, you would require a certain 3rd party which could do all that on your behalf, at a certain price, of course. We would call that agency or that 3rd party as a travel agency. Similarly, you can open up your own travel agency, if you think that you have the required resources and the knowledge to fulfill the requirements of the people.