To send an invitation to a meeting or to reserve a slot in your calendar in order to devote time to a client, you can use ' arewedoing events.
First, search for the customer we want to make an appointment with and click on the Events icon. On the right hand side any meeting which has already been held will appear, to create a new appointment click on the Add Event button.
From the window that pops up we can add a subject to the appointment, set a start and end, invite more people, add a description, etc. ...
If left unticked, no invitation will be sent to the recipient; otherwise, ticked contacts will receive an email with an invitation to the event.
In the following video you can see how to create an event related to a contact in 'arewedoing: