On your dashboard you can find list of menus on your left side

by clicking the Leads menu shows you the list of menus on selection of leads takes you to the leads page view. Where you can find the list of contacts available, By selecting the contact takes you to the detailed view of lead and select “enroll into automation” icon   which asks you to select the automation name from the list by clicking it makes you to enroll the particular lead into an Ongoing, Paused automations.