There are two ways to keep unwanted users away:
1. Block individual users
You can block individual members to prevent a contact from that person permanently. This can be done through the respective profile (see under options menu) or directly in a conversation in the title bar options menu. If you have blocked a person you will get no more messages, likes, profile visits or news from this member. The blocked member can still view your profile.
An overview of all of your blocked profiles can be found under Settings > Blocked members.
2. Exclude certain groups of people
Under Settings > New contacts in the section Privacy you can specify who can contact you. Existing contacts are excluded. You can determine for example that only people that match your filter may send a new message to you. Also you can choose if only people from your country can get in touch with you.
Example: You're looking for men who are 20-30 years old and come from the US (assume you live in New York). Only this group of people should be allowed to write to you. Choose in your filter "only male" , "20 years to 30 years ", "Only people matching my filter " and " Only people from my country ".