By providing liquidity to a trading pair of tokens, you will help the exchange execute faster and better. In return, you earn some of the trading fees and can further enhance your earning via rewards.
You can earn 0.28% of your share of the daily volume by providing liquidity to a pair of tokens. Not only do you earn from it - you also contribute to the ecosystem and provide a tremendous amount of value to it. You can select one or multiple pairs of tokens you want to provide liquidity for and every time a swap is made, you receive your 0.28% proportionally to your share of the pool.
If your proportional share of the pool is USD 1 million out of USD 100 million, you will receive 0.28% of 1% of the daily swap volume. If the swap volume is USD 200 million, you will receive USD 6,000 per 24 hours for depositing to the swap pair pool. You can, of course, deposit a much smaller amount than USD 1 million.
Siennas AMM is dual and you can deposit tokens for equal amounts in value on each side of the pair.