The DJ turntable is used to spin records and is essential to becoming a DJ. Different turntables have different features, such as torque, pitch adjustment and tone arms. The torque refers to the strength of the drive mechanism. The more strength, the faster your records will start spinning, allowing you fluent changes within a song. The pitch adjustment alters the speed and tempo of the record you're spinning on the turntable; the tone arm is what is used to scratch a record. Typically, straight tone arms are easier to use, because they won't skip on the record.
A DJ mixer is used to crossfade and adjust the volume between two turntables. You can also use a mixer to create pre-recorded DJ mixes, which you can sell at your venues. Inexpensive mixers usually only have two channels, preventing you from producing more distinctive sounds, like scratching.
The most important piece of equipment that's required to become a DJ is a good set of quality speakers. Even the best DJ sound systems hooked up to the most high-tech amplifier will sound terrible if the speakers are poor quality. While you can get by with inexpensive turntables, mixers and beat machines, you should have high quality speakers. Typically, bigger and heavier speakers almost always sound better than smaller speakers. Consider the impedance, power handling and sensitivity specifications before purchasing speakers---the higher the better.
An amplifier is attached to a speaker and boosts its volume. Quality amplifiers leave out distortion or coloration while using the least amount of power. When you're looking at the specifications, choose an amp with high wattage.
Beat machines are also referred to as drum machines, because they use electronic drum beats to create a continuous beat or combination to be played throughout your performance. Look for a beat machine that you can hook up to an external hard drive, so you can save beats to it. This will expand your beat library exponentially.