My name is Alex, I'm a guru here at Shopify!
Having a buy button directly on the home page isn't a feature included with that theme, but you can add that functionality any number of ways! Here's some third party paid themes that come with that feature built in:
If you'd rather not change your theme, that's totally understandable! I might recommend an app in that case - check out Add to cart button | Sales BOOSTER for that function, which also includes customization options for those buttons!
Hope that's helped! Please feel free to give us a call or start a live chat at any time, we're open 24/7 for your convenience and always happy to assist!
Alex | Shopify Guru
I am using Supply theme. I also would like to have an Add to Cart button with quantity selector on my homepage. I was able to do so by but whenever i click the quantity button. it just seems like just you clicked on the product page and didn't change the quantity. It also does the same when i click on add to cart. It just takes me to the product page.