Hello, Leonardo Reyes
1. If I am not wrong you might be talking about social icons, those icons are images in .png type if you want in square you can create your own icon image in square and upload it, for more information those images are from https://www.flaticon.com, here you can create icons as you want.
But the remaining other icons in demos are from font-awesome icons.
2. Yes, buttons links can be sent to another section of the same page.
first, name the section ID at the top of every section in the customizer there is an input field with label ‘ID Name’. for eg: ‘contact_us’.
second assign any button you want by adding button link to #contact_us, which solves your problem.
