If you are referring to EOS https://eos.io/, it is publicly traded on several exchanges. You will need to acquire bitcoin initially, many ways to do so but without an idea as to your location, can't advise. If you're looking for an exchange to purchase, bitfinex would be best based on volume. https://www.bitfinex.com
So in short, acquire bitcoin (various methods), register for an account at bitfinex (fastest to get registered of several exchanges), perhaps watch a youtube video on how bitfinex works and trade bitcoin for EOS.
Bitfinex doesn't offer EOS to buy. Or at least. i cant find it...