How to create a field in customize and show that in header.php?

I am new to WordPress coding and learning this from stackexchange,
I am trying to create one WordPress website from scratch, in header I want to show contact information for example phone number,
I want to create a field in customize and want to display the value in header.php.
Is there any guide or tutorial for that? Any help will be appreciated. Thanks a lot!!
*don’t want to use plugin

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