In this photo the young couple on the right has arrived at station 5009 (the ninth station in the 5th arrondissement) on rue du Fouarre, behind the church St. Julien-le-Pauvre, hoping to return their bikes there.
No docking stands are free (I have just taken the last one, actually), but the other couple on the left has just started entering their numbers to borrow two bikes, so two docking stands will be free in just a minute. (This often happens at busy stations with lots of coming and going.)
On the right side of the bike there is a metal tongue which you slide -- or ram! -- into the slit on the docking stand. If you've made contact the light will turn yellow, then green and there will be two beeps to confirm that your bike has been returned. But if you fail to get the tongue all the way in the light will blink yellow and there will be lots of rapid beeps as a warning, so you have to try again, using brute force if necessary.
If by any chance the light should turn red (which happened to me once), then the return of your bike has not been registered. In this case you MUST ring the Velib' people and tell them what happened, otherwise your account will be blocked and you might even be charged for the missing bike. You can make voice contact through the built-in phone in the computer terminal (using the i for information function on the front side of the terminal), which in my experience works perfectly well unless you are at a busy intersection with very loud traffic noise, or you can phone them at 01 30 79 79 30.
Second photo: These ladies have just returned their bikes with no difficulties to Velib' station 12010 on Avenue Daumesnil in the 12th arrondissement. (I took one of their bikes a minute later.)
http://www.en.velib.paris.fr/trouver_une_station


