If you hold a British, EU, US, Australian, NZ, or Canadian passport, then you do not need a visa to enter Croatia.
Croatia is a member of the EU, but not yet in the Schengen Visa zone. However, in many cases, if you have a Schengen Visa then you can enter Croatia freely as well.
The good news is that the process of getting a Croatia-only visa or Schengen Zone visa is quite straightforward but should be done several months in advance of travelling! To find out more about visa requirements for Croatia and how to apply if you need one, simply go to Croatian Ministry of Foreign Affairs website. Or you can contact the Croatian Embassy in your country.