You can put it in a mailbox or take it to a post office. I live in Northern Virginia and have mailed it from DC.

There is a caveat with the click 'n ship - I've actually had 1 package that I shipped via click 'n ship - printed the label, physically drop it in the blue mail box - and have it never show up to the other side. The kicker is - the label only initially reads something like "usps has been notified of this shipment, etc." - so technically only proof of printing the label, no proof of shipment - I got SCREWED on that one so anytime I click 'n ship to strangers (assuming some degree of trust some folks I know, board members here inclusive) - I take it to the Post Office and have them scan it so they've taken possession of it - and it's logged in the system and reflected online.