The only way to cock a M&P or Glock or similar striker fire pistols is to rack the slide to charge the chamber with a round. This makes the gun ready to fire in all respects (providing there's no thumb safety). There is no hammer to manually pull back like on a 1911 type pistol. With a double action semi-auto pistol pulling the trigger will fire the gun, hammer cocked or not - DA/SA. When the first round is fired the slide will come back, charging a round in the chamber & cocking the gun. From then on until a mag change after the last round is fired the trigger pull will be shorter & lighter. With a single action only like say a cowboy type revolver like the Peacemaker the only way you can fire the gun is to pull the hammer back for each shot.

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Former USN, Retired US Army