How should I learn classical music

I'm recently got into classical guitar been playing for 6 months now but I barely know anything. As a medical intern my schedule and budget is really tight to afford classes right now so I mostly turn to internet. How should I go about learning the instrument and music theory. I plan on learning other instruments too(once I'm confident with guitar)

I don't know where to start and how to practice properly. In what order I should learn theory and practice?

I'd appreciate any help or suggestions thank you!