Simple past and present perfect tenses

 You use the simple past tense when an action is completed. It can be: 

• a past habit 

He went to the gym at seven every evening. 

• a past situation (using a stative verb) 

He was a smoker in those days. 

• when you refer to research completed at a specific time

The study revealed that, in 1998, 35% of children played violent video games. 

• You use the present perfect tense when an action is completed, but it is still relevant to the present situation.
• The present perfect tense is formed with have + past participle.

He has lived in Australia for two years.