The first thing you should do is start doing a bunch of intermediate day hikes so you can develop your sense of effort and time when outdoors. A day hike is exactly what it sounds like: drive to trailhead, do the hike, drive home.
I would download an app like AllTrails and just find local hikes you can do of varying length and elevation. It's really important to develop this intuition because otherwise you have no idea how difficult something is or how to even gauge your own capabilities. This will also give you a good idea of the standard layout of national parks, trails, wilderness areas, trailheads, and so on. Take note of how much water you consume, how your feet feel, if you're developing any pains or aches, etc...
Once you have done a fair bit of these, then I would start thinking about getting some backpacking gear and doing some easy overnighters. This might sound pretty involved for what seems like a fairly benign activity but the reality is that HIKERS use virtually all of Search & Rescue's resources. Not the crazy basejumpers, climbers, white water rafters, or the million of other extreme sports. Mother fucking hikers. Three reasons: dehydration, fatigue, or injury. It's very easy to be in over your head, especially when you're dealing with variables like altitude or tundra-type climates
