The best thing to do is remain calm and don't panic. Try to assess the situation and take a few moments to observe the ghost. Are they trying to communicate with you? Is there a message they are trying to convey? If you feel comfortable, you can try to communicate with the ghost. Some people say that talking to the ghost and asking them to leave can help them move on. However, if you don't feel comfortable doing this, you can always contact a ghost hunter or paranormal investigator who may be able to help.
If you see a ghost, it is important to first ensure that your safety is not in danger. If you feel scared or threatened, it is best to leave the area immediately. If you do not feel in danger, you may want to try to document your experience with photographs, videos, or notes.
This can help you remember the details of your experience and can also provide evidence for other people to evaluate. If you feel that your experience is distressing or affecting your mental well-being, it is a good idea to speak with a professional such as a therapist or counselor, who can help you process your experience and develop coping strategies.
Additionally, it is worth noting that many people believe that ghosts are not harmful, and are just lingering energy or spirits of deceased people, while others believe that they are nothing more than the product of imagination or hallucinations. It's important to keep in mind that there is no scientific evidence that ghosts exist, and many supposed encounters with ghosts can be explained by natural phenomena or other non-supernatural causes.