Let people find your company on the stock market. The more buyers and sellers there are for your company shares, the more trading takes place. The shares flow readily, so investors are willing to invest in your company because they know they can sell the shares when they want to.
Like any market, this is where you buy and sell new and second hand shares. The stock market brings together buyers and sellers on a trading platform. Share prices reflect supply and demand. When you have shares, you part own a company: either you benefit from its success and gain growth and/or dividends; or suffer its failure and lose your money.