Right, now how to condense thirty-something years of navigation experience into a few words
Firstly, I remember being in your shoes vividly. Staring at a huge, laminated chart covered in arcane symbols and areas and wondering how I would possibly cope. The answer is, you just do.
There is nothing sacrosanct about straight lines. Yes, they can be the fastest track between two points, but if you hate flying so much that you want it to be over quickly then you have maybe chosen the wrong hobby.
Training flights are generally at around 2,000ft as the instructor doesn't want to waste your time dragging an underpowered aircraft up to more sensible levels. Once qualified and the master of your own fate - higher is better. (Caveat: not into clouds or airways of course)
Once above 3,000 you can virtually ignore the GA airfields on the chart and for the purposes of travel just overfly them as if they didn't exist. This does not apply to gliding sites.
Most larger airfields have some airspace of their own. Marked Class D. You are welcome to fly through this airspace, but you do have to ask nicely first. Until you hear the magic words "Cleared to enter ... " you stay outside. This may entail an orbit or two whilst you wait for something to happen. And there's the issue. You will find some pilots who take Class D transits as a badge of worthiness and will scoff at anyone who doesn't fly straight through every Class D in their path.
However, if you are planning on a transit, you also have to plan what to do when it is refused for controller workload or some other reason. i.e. you route around it. The thing is, if you compare the flight time for straight across v going round the edge there is generally only a minute or two difference. And if you do end up with a couple of orbits before being cleared then that difference vanishes or reverses. That said, it's fun flying directly across a major airport once in a while, Stansted is my favourite.
Military airfield have their own surrounding zones (MATZ or CMATZ) which look like the zones around big airports, but are actually not Class D. You can fly through them with impunity, but that isn't great airmanship, so you will actually call them and ask for a MATZ penetration which they will happily grant, passing any useful traffic information at the same time. As always there are exceptions. Brize Norton has Class D.
For high entertainment value Lakenheath with their own, individual, mid-Atlantic interpretation of communications are to be recommended.
Don't overfly glider sites with winch launching. Not advised.
Pay attention to your vertical nav as well as the usual horizontal. UK airspace is a total bog-up, and little fillets of airspace droop down from above with depressing regularity. Conventional nav is a pain as the charts aren't simple to decipher, SkyDemon (other apps are available) makes this simple
We are urged to "Take Two". This means remaining away from controlled airspace by 2 miles or 200 ft (vertical). Best you do this for now.
Have I missed anything? You bet. Others will be along soon and hopefully will discuss Danger and Restricted areas.