There is no simple answer to your question.
The tense of the verb in each sentence depends on the context.
The active/passive question is more complicated. When I was at school, half a century ago, it was almost obligatory to use the passive voice in most forms of academic writing, especially in fields that were, or thought they were, scientific. Things are more fluid today.
Try to find out what is generally accepted in the field in which you wish to write. If you are still at school or university, ask your teachers/tutors/lecturers/supervisors what they recommend.
Student or Learner