If you want to find out how to buy stocks in foreign markets, read Currency Exchange FAQ: How do I buy US/HK/CN shares with SGD (or your home currency if you are in other countries)?
Don’t exceed the number of shares indicated in the circled part when inputting quantity.
*** Max Qty to Buy (Cash)  does not show the amount of funds you have but the max number of shares that can be purchased with your cash at the price input in the order form. For example, ...