Setting up projects helps you to allocate your time entries more easily. 

Note: a client can be assigned to many projects, but each project can only have one Client.

In order to create a project please click the Button Projects (1) on the left side of the navigation bar. From here click on the Button up to the right Add Project (2):

This takes you into the Create Project page. You can name your Project and choose your Client.

If your client name doesn't currently exist, you can also directly create a new one.

In the Additional Settings you can decide if all your project times should be Billable (you can still manually edit your times to non-billable of course). There is also the option to choose between Task-based time budget and Manual time budget:

In addition, you can also create a new project directly in the the Timer (1) area. To do this, simply click on Select Project (2) and then Create Project (3):

You can also later sort through your projects with different filters: