How to add a Squarespace checkout link to Leadpages

Hello,

Two questions:

I am just getting started with Squarespace, so I already have a bunch of sales pages through leadpages. I need to connect my "buy now" button to the checkout page for that item in my Squarespace store. What kind of link can I use for that button? For instance, when I was using wordpress, I simply added the product item number at the end of the checkout link, and it took the buyer directly to checkout. That's what I need to happen, if that makes sense.

My second question is how to hide a product but have it still be live. So for a product I don't want to appear on my shop page, but I want people with the link to still have access to, what code do I need to add for that product?

Thank you!