You can add your website on the "Create A Post" step by tapping the 3 dots above your keyboard, then "Create post from a webpage." The website URL will then show up in the caption of your post. Once shared to social media, the caption link can be clicked to launch your website.
You can also add your website directly on the final share screen in the caption of your post.
Tip: If you start with a link (no text or photos) in the "Create A Post" screen we will grab metadata from your website to pre-load the "Create A Post" screen with some photos and/or text to save you even more time. You can update the primary or body text as needed before you share your post.