Your post doesn't say if you want to travel on trails or on roads. They are somewhat different forms of backpacking. Once a person has experience, road walking is more difficult than hiking on trails as the logistics are more difficult. It's also more expensive as people seem to spend about 2/3 of the nights in a motel.

Either way, the way to get started is to start gaining experience. Start walking almost every day no matter what the weather, except for obvious extremes. This will help get you in shape and you will learn what type of clothing is needed. Road walking clothes are somewhat different than backpacking clothes.

I have a foot in both camps, but I think I'm one of the only ones on this forum that has a big foot in the roadwalking camp. If that is your interest, you can poke around in the blog in my signature.

Whichever type of backpacking you prefer, things you read won't be meaningful without some experience. Start planning short hikes, and then short overnight trips, even if the overnight part is in your backyard.

Before taking off on a long trip of either type, I'd suggest a training trip long enough so you have to resupply food a couple of times. For backpacking, three nights out between resupplies works well for new people. The distance isn't so important and depends on the terrain. Even five miles a day is enough. For roadwalking, if you are going to be anyplace in the western half of the United States, being able to travel 75 miles without water is imperative. This means having a pushcart and being able to walk 25 miles a day for three days in a row.

Before you buy any gear, I suggest you discuss it here. Most new people waste money buying gear they don't need and gear that is too heavy.