The distinction between the Present Perfect and Past Simple is one of the most common hurdles for English learners. While both refer to actions that happened in the past, their focus is entirely different.
Past Simple
Used for completed actions at a specific time in the past. E.g., 'I visited Paris in 2018.'
Present Perfect
Used for actions in the past that have a connection to the present. Time is usually unspecified. E.g., 'I have visited Paris.'