DJ mixing is all about creating a continuous groove that keeps the
dance floor grooving. The DJ blends the end of one record into the
beginning of the next by lining up the beats, bars and phrases of the
two records and then making a smooth transition from one track to the
next.
Beats, bars and phrases are the building blocks of modern music - the
beat is the constant pulse which is present in every song (even when
the drums aren't playing). Beats are most easily identified in House
or Garage tunes when the bass drum thuds once on each beat. The speed
of the beat is called the "tempo" and is measured in beats per minute
or "BPM". A slow tune (R&B or Hip Hop for example) might have a
tempo of around 98 BPM, while faster tunes (in Drum n Bass for
example) can reach a tempo of 170BPM.
To get started, choose a tune and play it on the first deck, then
choose a second tune (roughly the same BPM as the first) and play it
on the second deck but without turning up its volume in the main mix,
so that you can hear it only in your headphones.
When both records are playing together, it quickly becomes clear that
the beats of the two records won't stay in synch unless they are
running at the same BPM. Use the speed control (or "BPM Slider") to
speed up or slow down one of the two records until the two BPMs are
the same.
To perform a simple Drop Mix, when the first record gets near its end
start the second record from the beginning and, in order to make a
smooth transition, use the "cross-fader" (the sideways fader at the
bottom of the mixer) to switch from the first record to the second.
To perform a Beat Mix, the DJ has to physically manipulate the records
so that the beats of both tunes line up in synch. When mixing with
real vinyl on a deck with a slip mat, this means he has to "grab" the
record, by stopping it physically with one hand on the surface and,
making sure the needle always stays in the groove, wind it forwards or
backwards (but without ever pressing too hard so the platter
underneath doesn't stop).
If you are interested in exploring the craft of djing further you
might want to look at more detailed resources on dj skills and dj
courses
Make Beats on Computer Fast and Easy: http://www.sonicapro.tk/