Slovenia is a member state of the Schengen Zone. All Schengen countries issue Schengen visas under the same conditions, taking into account the interests of the other Member States. A visa issued by one Schengen state is valid for all other states in the Zone which allows visits to the multiple countries within the Schengen Zone.
If you need a visa to enter Slovenia, you can obtain one from the Slovenian embassy or consular office in your country. If there is no Slovenian consular office in your country, you can apply to the consular representatives of any Member State of the Schengen Zone.
Since the information on visa requirements to enter Slovenia can change, it is best to enquire at your country's foreign ministry before leaving, or you can also check the situation at the Slovenian foreign ministry, where information is provided in English. And remember that when your visa is approved your passport must be valid for at least another six months.