In short infinitive is a basic form of verbs which is used in vocabularies. In English infinitives are "to be", "to do", "to take" etc.

Perfective and Imperfective are aspects of Russian verbs. Each Russian verb belongs to one of those aspects. Very roughly Imperfective Russian verbs have functions similar to English Present and Continuous tenses while Perfective Russian verbshave functions similar to English Perfect tenses. (Russian produces new verbs where English just changes tense.)

I think such information about English you can find in any English school grammar book.