Mermaid Swap is a new age DEX Platform with its presence across multiple networks. You can only swap tokens on Mermaid Swap if there is enough liquidity for those tokens. If nobody has added much liquidity for the token or tokens you want to swap, it will be difficult, expensive, or impossible to do so.

Providing liquidity will get you LP Tokens, which will earn you rewards in the form of trading fees for making sure there's always liquidity for the exchange to use.