The Pluperfect Tense in Croatian, also known as 'pluskvamperfekt', is used to describe actions that were completed before another action in the past. It's like saying 'I had done something' in English.
To form the Pluperfect Tense, you need to remember two things: use the imperfect form of 'biti' for the subject and combine it with the past participle of the verb you want to use. The past participle will change depending on whether the subject is masculine, feminine, or neuter, and whether it is singular or plural.