Individuals in your CRM are comprised of all your contacts. Leads are individuals that have been assigned a Lead Source. If you don't know the correct Lead Source you can still mark an Individual as a Lead by choosing the Lead Source 'Unspecified'.
If you remove the Lead Source from a lead it will remain as an individual.
Leads appear on most Dashboards with the most recently created at the top. They also appear in the leads section of the app.