Has a commercial airliner ever crash-landed in an ocean? They have rafts and life jackets on board and before takeoff, passengers are explained how to use that equipment, but have any evacuations ever happened successfully?
Yes, commercial airplanes have landed or crash landed in water many times.

If I am not mistaken, you are asking about scenarios when the on-board life jackets and life raft are used.

Here is a list of water landings. Examples when a life raft was used are (in addition to ratchet freak's mentions):


  On 22 October 1962, a Northwest Airlines DC-7C with 7 crew and 95
  passengers made a successful water landing in Sitka Sound. ... The
  plane stayed afloat for 24 minutes after coming to rest in the water,
  giving the occupants ample time to evacuate into life-rafts.
  
  In 1993, China Airlines Flight 605, a Boeing 747–409, ended up in
  water after it overran runway 13 ... All of the 396 occupants donned
  life-vests, boarded the eight slide/rafts and no fatalities resulted.