Leads are your potential clients. They have, in some way, interacted with or reacted to your marketing efforts.
For example, called you, left a phone number, or provided their contact information in any other way for further communication.
It, of course, does not mean that they will become your client, but they have already shown interest in what you do. The rest depends on your employees. When a lead becomes a client, you can transfer it to the new category. To do so, go to the Leads tab, choose the lead, click an icon with three dots on top and choose Edit. The lead status will be changed to Done in the card. After clicking Save, the system will suggest to move this lead to clients or delete this contact by marking it Poor.