Most cheap flight tickets are not cancelled or rebookable. If you have bought a trip and cannot go, you can contact the internet travel agency or airline where you made the booking to check if there may be a solution. If you know in advance that you need a cancelable flight ticket, you should buy a more expensive "flex" ticket directly from the airline. 

It is important that you review your insurance cover before booking flight tickets so that you know what applies if you cannot travel. A simpler travel insurance is usually included in the home insurance or if you pay for the trip with a debit / credit card. There are also supplementary and more comprehensive insurances to buy directly from the insurance companies or from the internet travel agency / airline when you book your flight ticket. 

Buy your travel insurance with FOREX.