You can easily add an event to the diary. Open it through the tab on the navigation bar.
First, find the engineer/date/time for the event, click on the time you want the event to start and drag and release to the time you want it to end.
If you wish to create a morning or afternoon event click the AM or PM sections at the top of the daily view. To create an all-day event, click, hold and drag from the top of AM down to the bottom of PM.
When you release your mouse button a sidebar will open on the right of the page. This is where you use the tabs, forms, and dropdowns to create your event.
Navigate through the tabs across the top of the 'Add new event' sidebar. 
Fill in the form with the relevant information. Click 'Save' and the new event will appear in the diary.
Or continue reading this article to see the different types of events:
Normal - This will allow you to type a description and notes without choosing a property, or template. This means you can use this to remind the engineer of their annual progress meeting, or that they have the afternoon off for example.
Estimate - This is the form you will use when adding an estimate to the diary. It will give you all the relevant spaces to put the details the engineer will need.
Job - This is the form you will use when adding a job to the diary. It will give you all the relevant spaces to put the details the engineer will need.
Fill in the form with the relevant information. Click 'Save' and the new event will appear in the diary.