To add a new customer, task, project or any other information relevant to your business you go into the page "Registers" in the menu on the left hand side and click on a register dedicated for the specific information you wish to add.
Then you click on "+ Add", fill in the form and press "Save".
Exactly what information you need to fill in depends on the structure of the register.
Some of the registers are available in the system as standard (for example, "Customer" and "Task"). If you are missing a register you can add it in "Register Settings" under "General settings" (the gear icon at the top right corner) by clicking "+ Add".
Note that you will only be able to choose customers, tasks, projects and other information you add to your registers in your shifts if a specific register field is added to your shifts.