Some people are fortunate enough to get free airline tickets to use for travel. It's not easy to get these free tickets. They are mostly given out during promotions. For example an airline has revamped its fleet and wants to attract fliers, they will give out tickets. These tickets may be valid only between certain destinations, so they may be restricting in that sense.
Sometimes a ticket can be given as a way of apologizing for a cancellation on a previous flight. Sometimes the travel agent may be acting as an airline agent and might be given some tickets give out as a means of advertising and attracting potential customers. For example if an airline is introducing a new route, or a new fleet of aircraft.
Sometimes someone could get free airline tickets by winning a raffle or something of the sort. The problem with these free tickets is that they have many drawbacks and limitations when it comes to utilizing them. For example, they might only be valid for a certain number of months, they could be non transferable or might be one way and you have to organize your way back. They could also be to a destination that you have no interest in.
Anything that's free is always very attractive, and unless you are flexible and don't mind the restrictions that come with the tickets, you are good to go. And again, as with anything that is this attractive, make sure you always read the fine print. Ask any questions you might have for the person who is giving you this free airline tickets.