'Seen' is a participle form of the word 'see.' The verb form of 'seen' indicates that someone has visually observed something or visited a place. It can also refer to being witnessed by someone. For example, you could say 'I have seen the Grand Canyon,' to describe visiting the area.
1. She has seen many wonders of the world in her travels.
2. The students had seen the consequences of their actions.
3. My sister had seen a large volcano during her travels.
When using the verb form of 'seen,' pay close attention to when the action occurred. Depending on the context, it could indicate a past, present, or future action.