Now, every modern DJ needs a CD player - prefferably two. Many of the most modern DJs use turntables but as vinyl is slowly but surely dying out, CDs are the best option. Now, if you just want to do straight back-to-back song playing, you can probably use your hi-fi and another CD player. All you need to do is connect the headphone socket or output socket into a mixer (see mixers page).
However, if you are doing professional mixing where you join songs that are similar speed together, you will need a special DJ CD player with pitch control. Basically, the pitch control allows the speed of the CD to be altered usually by 8% or 16% each way. This is just like turntables.
For professional use, I would advise getting a double deck. A great place to get DJ gear, including CD decks, turntables, amps, speakers, mixers, lighting, is Sapphires Sound & Light in London, UK.