I guess at that point you just need to start doing it. I have a lot of outdoorsy types in my family and we've been doing long, multi-day backpacking trips most summers since 1998. On my first trip I bought a cheap sleeping bag, pad, and backpack and relied on the more experienced people in the group for everything else. The shoes I wore were terrible and by the time we got back to the car on the end of the 4th day I could barely walk my feet were so blistered. For the next summer I saved up and bought a really nice pair of boots which I still have. They're the most expensive footwear I've purchased in my life and worth every penny.

I can't recommend enough finding a group of experienced people to start with. You'll make plenty of mistakes and they'll help keep it from turning into a catastrophe. You'll pick up a lot from them while also figuring out what does/doesn't work for you. Probably five years after starting backpacking with my family I was the 'experienced one' leading a group of friends on a hike through the Smokey Mountains on the Appalachian Trail.

Start out car camping. My progression was:

1. Avid day hiker (10-16 mile hikes every weekend, 5-8k ft gain)

2. Car camping in Ojai (near Los Angeles). Drive in, setup your tent, chill, sleep, leave next morning.

3. Backpacking around LA on the trails from step 1

4. Thru-hiked PCT

5. Mountaineering / alpine climbing

Lots of people do the PCT with little hiking experience and are fine though. It's just walking, and there are tons of people to help you.

When we do an Intro to Backpacking weekend as part of our Spring hiking program, we tend to go in a relatively short distance to a lake/pond or something along those lines. And then will do one or two day hikes from there. This gives plenty of time to experiment with gear, setting up/breaking down camp, and so forth without the time pressure of having to get to some destination. (But you still get a sense of pack weight and so forth.)