Sometimes you may need to delete (maybe because you let your video-camera or TV-capture-device run too long) or maybe to apply a video effect to only a part of a clip. Kdenlive allows you to do so by splitting the original clip.
To split a clip, the normal way is to place the timeline cursor at the splitting point (you can adjust the exact position by playing with the "Next frame" and "Previous frame" buttons in the "Timeline Monitor"). Then press the right mouse button and in the context menu select option Razor Clip. (The razor cuts before the current frame, so the right strip will contain the frame you're standing on.) With this option only the clip in the current track will be split.
You can split all clips at that position selecting the option Razor All Clips in the edit menu.