Why do I see people I don´t know in my network?
In your network you see people that are related to you although you may not know them. Most likely, it´s an indirect relationship which could be family of a non-blood relative of yours.
You can know that relationships you have by clicking on the "View my relationship with him/her" link that is found in the list view or in the profile cards.
To only see the certain people you are interested in, you can create groups and specify those that are most important to you and would like to keep track of. View "Groups" in the help section to learn more.