What is the correct way to run a command after boot on ubuntu 18.04?

I need to run a simple batch of commands after the computer boots, something like

sudo thing
sudo thing1 -p

But for the life of me I can't figure out how.
I googled and googled and I kept finding the same thing: Place the commands into a /etc/rc.local or /etc/init.d/rc.local file. The problem is that none of those files exist on my system!
Furthermore, I have read that /etc/rc.local is deprecated anyway, so what the correct and simple way to do this?

I would like to know how to these two things:

• run a command after the computer boots



• run a command after specified user logs in, and run it as the given user

  
  

  (And make all that happen solely by editing stuff in the terminal, no GUI tools)

Thank you.