This is a Quidax feature that helps you stake your QDX. The QDX Vault gives you access to Airdrops (free cryptocurrencies that you would have had to buy on your own). All you need to do is buy QDX and stake it in the QDX Vault to earn free cryptocurrencies and other rewards.
The average amount you stake in the QDX Vault over the staking period will determine how many tokens you will receive.
Anyone in the world can use the QDX Vault apart from US Citizens and OFAC sanctioned countries