Gutenberg is the newest WordPress editor as a replacement for WYSIWYG or classic editor that WordPress uses for years.

Child theme is a theme that inherits its parent theme styles & functionality. The Child theme and its parent theme are connected, you can't install the child theme without the parent theme installed first.

These 8 steps are pretty simple to implement, there are more plenty more ways to improve WordPress performance, but they require more work and complex steps. Just try each step above carefully, you should get better performance.