At What Age Did You Start Socializing Your Puppy, and How Did You Do It Safely?

For those who’ve raised puppies, I’m curious about your socialization timeline.

At what age did you start introducing your pup to:

New people Other dogs Different environments Various sounds, surfaces, and experiences

And how did you do all of this safely before full vaccinations? Did you use controlled meet-ups, stroller outings, carrying them outdoors, puppy classes, or mostly indoor exposures?