If you need to block communication with another member you can do so through the Network Menu > Members and then clicking the 3 dot menu. You will be able to find the option to block the member here.
You can also block a member through chat. In the chat window with the member you can click the 3 dot menu and choose to block the member.
Once you've blocked the member, you will no longer receive notifications or private messages from the member. You will also no longer see their posts in the Activity Feed.
Please note that blocking a member will not prevent them from seeing your posts.