Hello,
Sliders are coming from the post type, you can create a slider from Dashboard >> Sliders >> Add new >> Add slider title, contents, button text, featured image >> Publish, and it will show you as a slider.
Thank You.

Hello Keith,
Here is our theme step-by-step complete documentation link below.
https://www.luzukdemo.com/docs/professional-software-company/
Thank You.

Hello Pavel,
Kindly explain your exact point about the posts in more detail. So we can understand it better.
Thank You.

Hello Kealauluwehi,
To change the header facebook social icon link follow the steps given below
Go to Customizer >> General Configuration >> Header Settings >> Social Media Icons >> Facebook Url(Change the link) >> Publish.
Thank You.

Hello Arisha,
Do you want to remove the home page static category sidebar? If yes, then add a given CSS into your Customizer >> Additional CSS.

.sidecategorie {
display: none;
}
Thank you.