WP Customize Control

I’m working on a theme and I want to be able to change text like you are able to do with the site title and the tagline. I’m quite new to developing WordPress themes so I’m not to sure whether going about this in the correct manner, I am using WP Customize Control I’ve set everything up in functions.php but Im unsure of what to do next. any help with this will be very much appreciated.

thanks in advance for the help.