Citizens of most of European countries can enter Serbia without visas for up to 90 days, including many other countries, so you should check, before travelling to Serbia, whether you need visa. For doing that, please visit the website of the Ministry of Foreign Affairs of Serbia.
In case you need visa to enter Serbia, please,visit following links for more information:
For more information regarding the issuance of visa, please contact diplomatic-consular mission of the Republic of Serbia in your country, or the nearest one. You can find the list of Serbian embassies around the world here.