Once you purchase any paid plan of WP Sticky Sidebar, you can use it forever. Support and updates are available for 1 year. You can renew your license each year to get another year of support and updates.

No. You will only be charged if you renew your license manually. You will get a reminder email before your renewal date.

Of course NOT! 
Your WP Sticky Sidebar plugin and all your settings will continue to work as before; however, you will no longer receive plugin updates including feature additions, improvements, and support.

If you are not satisfied with the plugin or it doesn’t work for you for any reason, you can email us at [email protected] within 30 days after your purchase and you will get a refund.

So this depends on what you want to make sticky and what theme do you use, but for example if you want your menu to be sticky, than you can examine the code (in firefox right click and “View page source”) and find HTML element in which your menu is situated. This element have some class or id, and that’s the Sticky Class we need. If using class than don’t forget to ad dot (.) in front of class name, or hash (#) in front of id. Twenty Thirteen default working class is “.navbar” without of quotes.

Read the full installation guide: https://premio.io/wordpress-premio-pro-version-installation-guide/