All countries have their own Visa requirements. Some countries issue visas right at the airport or at a border crossing point. However, it is more common to have an issued visa before entering other countries.
Prior to booking your flights, please read travel document requirements for entry into the destination country or for connection in the transit country. Also, please make sure you have got all necessary documents and visas. For more information, please visit http://www.iatatravelcentre.com/ and read the information available on the website of the Ministry of Foreign Affairs of your country of residence.