You can quickly create a lead in the "Leads" section (view "Leads" = vertical lines). Click on the "Quick Add" button and fill in the lead fields. Then click on the "Add" button.
In order to add a lead from a contact/company card, go to the "Lists" section. Open the contact/company card. There is a “Leads” tab on the left pane. Click on the "Quick add" button. Enter the lead name, the stage and the pipeline. Save it.
In quick adding leads required fields are not taken into account.