Slovenia is a subject to the Schengen agreement so rules for entrance to the Schengen area apply. Nationals of other EEA Member States (EEA citizens are nationals of EU Member States, Norway, Iceland and Liechtenstein) or Switzerland may enter the Republic of Slovenia with a valid personal identity card or passport and do not require an entry permit (visa) or residence permit.
A list of countries whose citizens must have a visa when crossing the external borders and a list of countries whose citizens are exempt from the visa requirement is available here.
In case you need a visa please apply for one at the Slovenian embassy or any Slovenian consulate in your country of residence. A list of Slovenian representatives is available here. Please start with the procedure as soon as possible.