Ableton's clips are used as the building blocks for music production. Clips come in two forms, audio and MIDI.  Importing audio or MIDI data into Ableton will automatically create a clip; audio clips will display a waveform, whereas MIDI clips will display MIDI data.  You can use clips in session view to plan your ideas, arrange a general song structure, or even plan a live performance by queuing up entire tracks.  You can look closely at clips via Ableton's clip view mode (hotkey: Shift + Tab). Clips can be merged, duplicated, split, and even color-coded to help clean up the aesthetics of your project.  Color coding clips can be helpful when identifying the different sections of your track, separating elements such as drums and melodies into a uniform color group, and creating variations to musical ideas.