Adding fixtures can be done in the Cargo tab of the Voyage Drawer by selecting the Fixtures button and clicking the + Icon above the list.
Charterer
Which Cargoes to connect (based on which Charterer is chosen)
Fixture Reference
CP Date
CP Form
The Cargoes list is empty at first until you have chosen a Charterer. Selecting a Charterer will show all cargoes connected to the Charterer in the list below, allowing you to select the ones you want in the fixture.
Clicking the edit-pen icon will open up the Edit Fixture modal where you can change fields and select more or de-select cargoes.
After clicking save you will be asked to confirm if the selected cargos can be changed to have the same charterer as the fixture.
The fixtures list has a separate button to collapse/expand the cargo list of all the fixtures with one click as shown below: