After logging in, PCB:NG will display all of your current projects ("boards"). First time users will either find that they have no boards, or there may be a sample project to help get acquainted with PCB:NG.
Since PCB:NG is about making your board, get started by clicking on "Create new board". Doing so will bring you to the PCB Tab.
Once you've created one or more projects, you'll be able to delete projects, or return to them by clicking on the project name.
Clicking on the PCB:NG logo from any screen will return you to the "Your Boards" page.