Immediately after you publish your post, a pop-up window will let you know the post is live, and it'll display an image preview of how it'll show up on your socials. Below the preview, you'll find the option to share it on your Twitter, Facebook, and Pinterest (requires log in authentication). You'll also find an option to copy the post link to add it directly to a platform.
Directly from the post in your Feed
Even if you skip the option to share your post after publishing, you can always do it directly from your creator page by clicking the share button on the post. You can also click on the post title and grab the post page URL to link directly to a platform.