Lukas, the verbs pisati, čitati , govoriti, učiti, ili raditi, for exemple , are "imperfektivni glagoli", and their action are not restricted by some times. But, upisati, zapisati, propjevati, povikati, uraditi...are "perfektivni glagoli" Their duration is restricted. You can "zapisati" only once. there is no duration of the action in this case. That is why they are perfective verbs. The verbs pisati, pjevati, nositi , voziti are "trajni glagoli". There is no brakes in their action. You can , for example write for hours. "Učestali glagoli" such are iznositi, odvoditi, poskakivati, zapitkivati.. have the action which can be repeated many times no mater about their frequency. And finally there are three groups of these verbs: 1. "Trenuntno svršeni", which action is finished in a moment: leći, sjesti, reći, udariti... 2. "Početno svršeni glagoli" which describe an action in the start such are zapevati, zaigrati, poći, krenuti... and finally 3. "završno-svršeni glagoli" whish describes the end of some action: ispitati, napisati, uzorati, posijati, pročitati. So, if you need more explenation , let me know.

Ako želiš, mogu ti održati par časova vezanih za gramatiku. I objasniti ti sličnost između par balkanskih jezika, uključujući i hrvatski. Dobro poznajem gramatiku, jer sam završio fakultet za to. If you want, I can give you some lessons about grammar. I can explain you the similarities between several Balkan languages, including Croatian. I know grammar extremely well, 'cause I've finished faculty for that. Let me know if you're interested ! :)