The following overview provides you with what you should know about the Greek verb system:

• 8 temporal stages:
  → Present: 1 form
  → Past: 4 forms (paratatikos, aorist, perfect and pluperfect)
  → Future: 3 forms (simple future, future continuous and future perfect
• 2 basic verb conjugations (present stem and aorist stem)
• 3 voices/diathesis (voice of the verb)
• 2 auxiliary verb
  είμαι (engl. I am, „to be“) and „έχω“ (engl. I have, „to have“).
  „έχω“ (engl. I have, „to have“) is used when forming the perfect tense and pluperfect.
• 3 modes (signalling modality = signalling intention of speaker):
  indicative (mood of reality, neutral/objective), conjunctive (subjective opinions, emotions, wish, polite requests), imperative (mood of commands, prohibition, orders, requests)
• 2 participles (present, perfect)
• infinitive with limited function

If you are not familiar with personal pronouns, you may want to look them up here.