To create a new custom networking group...you must first be logged in...

On the home page, underneath your profile picture, there is a link for My Groups.  You can either click on the link to see your current groups or under the Applications tab on the home page you can drop down to "Networking Groups" and click there.

When you are on the My Networking Groups page you can there manage your existing groups or Create a Custom Networking Group.  To do so, click on the link in the right hand corner.

On the Create a Custom Networking Group page, you will be able to title your group, give a brief description, and set the privacy of the group. Click on the Create button and you are finished.

It will bring you to a page that will help you get your group started and suggest ideas to make your group interesting.