New York City Metro

There is no online option for purchase, but you can buy it at many locations and on buses and vending machines.  I bought my 7 day pass from a kiosk in the La Guardia airport.  They charge $1 for a new paper Metro card and apparently cannot reload an old card with an unlimited pass from a kiosk.  You can add cash value to an old Metro card.  The La Guardia kiosk only took credit and ATM cards and not cash.

For buses, feed the card into the slot with the "M" facing down and towards you.

For subways, slide the card like a credit card and push the turnstile.

Subways usually have express vs. local routes.  The express skips stops and often, but not always, comes at the opposite side of the same platform.