If you have users with calendars connected to FLG an appointment can be booked directly from a lead.
Please see getting started with appointments if you need to connect a calendar first.
To book an appointment sel ect New > Appointment fr om the lead summary page.

You can then customise the appointment details or select an appointment type. Click on Next to proceed.

If creating a custom appointment select the user. Confirm the date and time for the appointment.

A summary of the appointment details will be shown on screen. Click on the back button if you need to make changes, otherwise click on Save to continue.

The appointment will then show on the lead summary page and in the connected calendar.