Leads can be created against customers to unveil the business potential. You can create leads from CRM->Add Manage Leads. Leads can be created with basic contact and personal details of a company or a person. With that we can keep the activities of calls and meetings from one place.
Tasks can be created for leads, which helps to monitor and provide additional tasks to staffs to followup the lead. You can also add attachment to leads which will be helpful to keep the documents and open easily from the source.
A lead can be converted as customer with the lead contact and personal details. Also you can keep the documents and tasks remain to the customer.