Hi, Welcome to the forum,
You can usually find the answer to your question by using the forum search function, since this topic has been covered several times before!. I managed to find all of the answers to your questions within 10 minutes of looking!. It's all here!.
Try reading
THIS THREAD since it discusses Soundcards in the topic and there are a few suggestions. Also try searching the forum using the word "SoundCard" and "Sound Card" for other threads.
Either way you are going to need to buy an Audio Mixer, Amplifier and suitable speakers if you intend on setting up a disco professionally. If you could tell us what type of venues and gigs you are planning to do then we would be able to help you!. Just starting a topic with "What do I need" could leave you open to replies that are over the top for what you actually do require!. For instance I could recommend that you buy a £10,000 audio system, when you only intend on doing School Disco's and a £500 system would be enough!.
For more information on what equipment you need to buy to start out properly then
This Thread gives you an idea of what Amplifier and Speakers you would need and how much it would cost.
Given the limited information that you have posted, it would be impossible for anybody to help you

. For instance from your post I assume that you already have Amplifier and Speakers?, what connections does your amplifier have?, How sockets do your speakers have?, how far do you wish your speakers to be from your amplifer?, what make of Amplifier and Mixer are you using?.
Just to say "What cables do I need", gives around 500 possible combinations! since different manufacturers use different sockets to connect their equipment together. Its not that people don't want to help you, its just that they CAN'T help you because you aren't given them enough information to answer you!. And Posting or demanding "PLEASE REPLY TO ME!" is also likely to get you ignored in the future.
I need to have more information about your set up before I can answer your question, and the information you give will need to be more than 2 lines!.