How to backup a MacBook Pro step by step?

You have 2 options:

• Manually copy and paste the data you want to an external drive or
• Use Time Machine Back up your Mac with Time Machine - Apple Support

I do have an old Time Capsule and I use Time Machine for an emergency and for convenience (it's just easy), but when I need to reinstall everything, I use the the good old command C command V for the data, and for the macOS and apps I do install them from zero, not recovering from backup. That's my way of keeping distance from old system files and settings that can give me a hard time, you know.