When claiming a lead using a sequence select the Sequence Icon from the bottom of the Lead Card.
Select the sequence to be used from those available. *NOTE Sequences require certain lead information to be present in order to be used (ie eMail address and phone number). As a best practice we recommend building sequences that are all eMail, all Text, and mixed - in order to ensure you will always have a sequence available for every lead.
Your sequence is now started. To check on the status of the sequence, or to manually terminate a sequence, open the Contact record, select the sequence gear icon, and the sequence will open.