Launch Ableton by clicking on the black and white "Live" icon and allow it to start. Create a new Live set by clicking the "File" menu, followed by "New." Click "File" again and select "Save As." Choose a file name and save location for the set and click "Save."
Click the triangular arrow in the upper left corner of the screen to expand the file browser. This will allow you to search the various folders on your computer for the song files you wish to use in your DJ set. Click the Create menu and select "Create Audio Track." There should now be two audio tracks in your main window. These will represent your two "Decks." Think of each one as an individual turntable or CD player.
Drag and drop your desired tracks from the file browser into the rectangular slots in the upper half of the audio tracks. Click the drop-down menu on the transport bar labeled "Quantization." Select "4 Bars." This will mean that your clips will only be triggered or stopped at each 4 bar marker.
Click the "X" button in the lower right corner of the Session view. This will add a cross-fader and a pair of "A" and "B" switches to the bottom of each audio track. Clicking the "A" button on a channel assigns it to the left side of the cross-fader; engaging the "B" button assigns a channel to the right. Click the "A" button on your first audio track, and the "B" button on the second. You can now play both tracks at once, and slide the cross-fader left and right to fade between them.
Create a drop by clicking the play button on your first track. Keep the cross-fader in the center position. It's important to know the structure of your tracks very well; you should know the "crescendo" point at which you should drop in your second track for maximum impact. As the moment approaches, wait until you are within 4 bars of the drop point. Click the play button on the second track and the triangle will start to flash yellow and green, indicating that it will start to play at the next 4 bar milestone. At that point, slam the cross-fader fully over to the right, cutting the first track completely and "dropping in" the second.