You will be able to add call manually from 
Global Data → Calls section or from lead contact card.
Click on the Calls tab and select "Add Call" button from the top right of the section
"Add New Call" popup will appear
Select Contact/Lead you would like to schedule calls with
Select the Event
Choose a Host by selecting any of the two options:
Round Robin → iClosed assigns a host according to the Event Priority or
Select Manually → and choose a Host from the drop down list
Click "Schedule call" and select time and date inside the calendar
Learn more about Contact cards here.