As you know Composer is a great tool to manage packages and their dependencies in PHP, while in Drupal 8.8 is going to more composer compatible, you can find composer cheatsheet in the following.
Composer
Sometimes you need to apply the patch in Drupal 8. as I wrote here after Drupal 8.8, Drupal is more composer friendly CMSF, So you can easily apply custom patches without worry about how to keep the patches available in Drupal core updates.
How to apply a custom patch with composer?
first, you need to install cweagans/composer-patches which is a package to apply patches by composer. you can install it with