Leads are the entities constituting a first contact. Leads can be created by a system users or by a web-user. When a lead is created minimal info (name,email) is entered and the lead is (default) linked to the active system user, the owner of the lead A user configurable drop list is used to classify Status of the lead (Open, Replied etc)
A Lead can sometimes be an organization you are trying to make a deal with. In this case you can select "Lead is an Organization" and add as many contacts within this organization as you want.
It is useful if you are establishing a relationship with several people within the same organization.
If a someone creates an account through the website interface is Lead is automatically created, status is Open and the Owner is the webuser.
After registration the webform Addresses is called, where the web user can enter address information.The address is linked to the lead using the **Lead Name-Address Type** as ID.
If using the Cart functionality, items are ordered the Lead is Converted and a Customer is created using the Web-User Name. Because a Customer can only be linked to a webuser using the (foreign) ID in Contact, such contact has to be created as well.