How do I make customizable field? Like cover photo and Load More button

[ Moderator note: moved to Fixing WordPress. Please do not use Developing With WordPress for these topics. ]

Hello,
I am new in WordPress. I am working on my theme. I wanna learn how to make customizable field.
For example;
Left side is my theme, right side is other theme.

As you can see there is lots of customizable fields in other theme.
I wanna do same for my theme.
My theme has cover photo and profile photo and I wanna make it customizable.
Part of my theme;

And I need help for load button too.
I don’t wanna make pages, I wanna make “Load More” button but I don’t know how can I make.

This is my button;

Is there any article or video about these topics?

• This topic was modified 7 years, 5 months ago by closery.
• This topic was modified 7 years, 5 months ago by Jan Dembowski.