If you want to be a DJ, then there is some equipment that you will definitely need to have. There are several ways to set up a DJ gig but there is some basic equipment that every setup needs.
A CD turntable is a good idea, especially one that has a USB input. The USB input will allow you to also play digital files that are stored on an external portable hard drive or on a USB thumb drive.
At the most basic level you can just use a laptop that has some type of DJ software loaded onto it. There is computer software available for DJing using your computer, some of these programs are even available free of charge. It really depends on what features you are looking for as to whether or not you should use free software or buy software.
Even using this system, you will probably also need to have some type of audio interface so as to send the music to the sound system of the club that you are playing the music at; unless you are just doing a DJ gig for a small crowd of friends at home.
Different audio interfaces have different features and options for inputs and outputs. You generally don’t need more than two inputs and outputs for using it as a DJ. An audio interface really improves the sound that is being produced.
A turntable is another good idea to have if you want to be taken seriously as a DJ especially since the sound of music played off vinyl is still considered by many to be far superior to the sound of digital music. Of course, using a turntable means carrying more stuff to the venue and having to have music in vinyl form which may be more a bit limiting since newer music may only be available in digital format. Your selection of music may thus be limited.
If you do use a turntable, then you need to have a mixer and headphones as well. The mixer controls the audio volume, equalization (balance between frequencies of the music), and various effects for several audio channels.
A decent pair of headphones that are designed for a DJ to use is the way to go. These are better quality than conventional consumer headphones that you would use at home. Proper DJ headphones allow you to hear a greater range of frequencies and thus are much better to have if you are serious about being a DJ.
Today the turntable may not be as popular as the so called CDJ where CDs are used. The CDJs do also have USB inputs for attachment of USB drives or external hard drives. This is a large advantage if you want to have access to a wide range of music. In the early 2000s is when the CDJ really became popular. The CDJ often does have a vinyl emulator mode to replicate the sound of music played on a vinyl record. CDs though may not last very long and some DJs still prefer to use the traditional turntable.
You have some decisions to make regarding what sort of setup you want to have as to what equipment you need to buy if you want to be a DJ.