I think that the only way to get free airline tickets is to win them or receive them as a present. But it's easy to find really chip tickets, and if you buy them in advance, then you'll save a lot of money. When I plan my trip, I always buy tickets in a few months, and the price can be lower than 10 euros. It's almost free! So, if you want to go somewhere abroad, check sites of low-coast companies or other services like https://europefly.com/en. Prices there are reasonable, and you can find their tickets to almost any destinations.