Hi,
1) Basically, you can use classes in your article. This ‘Typography’ page is also an article, to see how each class is being used, you can go to Global Configuration > set Default Editor to None.
This template is built with T3 framework which utilizes Bootstrap 3, you can see full classes here: https://getbootstrap.com/docs/3.3/css/
2) It belongs to the footer module of JA Biz template, you can edit in 2 files:
[root]/templates/ja_biz/html/mod_footer/default.php
[root]/language/en-GB/en-GB.mod_footer.ini
3) For the slideshow, you can follow this topic
Regards