Hello 6Arashi9 and welcome to the community!
I'm sorry to hear that you had a negative experience in Second Life. There are a couple of ways you can deal with the situation, some of which has already been highlighted by your fellow residents:
Consider using the Block/Mute feature. The Second Life viewer, as well as all Third Party Viewers, has the ability to block/mute other residents. This will not only prevent you from seeing what they are saying, both in public and private chat, but will also completely block their avatar so you will not see them at all.
If you are a land owner, adding their account to the ban list of your land will also prevent them from accessing your personal space.
If you feel that the person is following you from place-to-place, it may be that you are visiting your regular locations and the person knows this.
If you are using a Third Party Viewer, you may wish to make sure that RLV is not enabled, as this can allow a person to track your location as well (the location for turning that off is different depending upon the viewer, and you will need to access that specific viewer's documentation for further assistance in this regard).
If, after the above methods, the resident continues to harass you, please file an abuse report under Harassment - Verbal Abuse and provide us with as much detail as possible—including as complete a list as possible of accounts used in the situation—so that we can better review the report.
We also have a handy Knowledge Base article to help guide you through the Abuse Reporting process. You may find this here:
I hope these tips help you! Happy future adventures through Second Life!