Page preloaders are useful if you have a big landing page or a lot of content and pictures, videos, so the visitors are “entertained” while the page is loading.
Call-to-action (CTA) buttons are buttons for your website / landing pages / e-shops to direct users to your goal conversion. This might be to sign up to a newsletter, add to cart buttons, create a free account, download buttons or anything you want your site visitor to do.