The best case policy is to go DIRECTLY to the EOS site https://www.eos.io/

Remember, this is your money.

You may get an error like this "US-IP detected, participation not allowed"

This is because you cannot buy in to the auction from the US legally (There are some pretty Draconic laws about IPO's here and a coin is still a public offering).

What do I do if I'm in the US?
Legally, wait. Buy when the coin has a defined value in 5 days.

What if I don't want to wait?
Buy from another country (or using an international connection). Bear in mind if you do this you are potentially violating US laws and EOS terms of service, this may result in losing 100% of your investment and could result in criminal penalties.

The EOS.io Site is down!?
No, it isn't ... it's getting more traffic than it can handle. Keep trying.