If you've got a gamepad connected, it will assume you want to use that, and disables the mouse cursor and keyboard.
I only found that out last night when I went straight from Rocket League to this, and it took me a moment to realise I needed to flick the batteries out of my pad to turn it off.
Since this is Bethesda, the only way to prevent that happening is to manually disable the controller (as you did) or manually edit the relevant ini file for the game (as I did). Unless the recent PC patch added the bloody obvious option to the control menu that should have been there all along.
You couldn't make this stuff up. Nobody with any sense would make a game that way, let alone in 2018. I remember having to manually edit autoexec.bat and config.sys to get some games to work, but that doesn't mean I think that sort of thing is the right approach when there's absolutely no reason for it. It's either malice or incompetence on Bethesda's part and it's a lot of one or the other because this isn't the first time - Fallout 4 was the same - so they know that it's a problem.
What am I trying to achieve with a CAMP?
Is it purely about being able to get at my stash without having to go to a petrol or railway station?
Not only about that, no. That's a large part of the point of a camp, but there are other uses for a camp:
1) You can build workbenches in your camp (as long as you have found and read the plans for them). It can be useful to have one of each workstation in the same place that should be at least relatively safe if you've chosen a good spot for your camp. You should find cooking, weapon, armour, chemistry and tinker workstation plans very early on in the game. A plan for a power armour frame is much harder to find and you probably won't get one early in the game.
2) You can grow food at your camp, as long as you have at least one of the relevant plant, e.g. when you find a tato in the game you could go to your camp and "build" a tato plant using that tato. You can harvest quite frequently (and use the harvest to "build" more of the same type of plant if you want). Most usefully, this can be used to make soups (after you've found and read the recipe for them or found one in the world and eaten it). Soups reduce thirst and hunger and they restore HP.
3) You can acquire purified water at your camp (as long as you have found and read the plans for a water purifier and a power generator).
4) You can build an adhesive farm using (2) and (3). You can use a cooking station to turn corn, mutfruit, tato and purified water into vegetable starch, which you can then scrap into adhesive. This can be useful since adhesive is used for a lot of crafting and repair. You can find enough if you explore and scavenge as you play, but it can be useful to be able to make your own.
5) You can fast travel to your camp for free. Even if your camp isn't your destination this will reduce your travel costs if your camp is closer to your destination than your current position because you'll only have to pay the cost from your camp to your destination.
6) If you build your camp in an area containing a resource (e.g. a mineable vein of something) you can (as long as you have found and read the relevant plan) build an extraction machine on the resource and gain some of that resource while you're doing other things.
For water and other resources, you can lock the purifier/extractor to make it difficult (or impossible if they don't have rank 3 lockpicking) for other players to steal from it.
You can also build traps and turrets to protect your camp when you're not there, but your best bet is to place your camp out of the way and especially not near a spawn point for anything hostile. Mine is on a ledge on a fairly remote cliff. Hardly any player goes there and hardly any hostile NPC can get to it or even get close enough to "see" it. I have very rarely had a few molerats follow me to my camp and burst out the ground inside it and I once had a super mutant wander to the top of the cliff and shoot one of my corn plants.
And if so, do I need to build a stash box in the camp? Or does the camp itself act as a stash box?
You need to build a stash box. If that's all you want, you could build just a stash box and nothing else. It's completely safe - no other player can access your stash box (unless there's a bug for that too). Other containers you can build are at best useless because they're only a connection to your stash. They might be worse than useless - some people have said that other players can access them and thus access your stash. I don't know if that's true.
Question about the workshops that you can pay to own - do thjese generate junk while you own them? Is that the purpose?
Only if you build the right kind of extractor and place it on the right kind of resource or build enough power generation and use it to power the relevant machine. If you hover over a claimable workshop icon on the map it will tell you what resources can be generated by it. If, for example, it says silver(1) then there's a silver vein somewhere in that workshop area and if you own the workshop you can build an extractor on that vein and it will generate silver over time. I have used two - the Gorge workshop to farm black titanium and the Poseidon workshop to manufacture fusion cores. It's of very limited use because the generation rate is extremely low and the storage capacity of the devices is very low (so you have to travel back often to empty them so more can be generated) and it only lasts until you leave the world or the workshop is taken off you.
Another purpose is to complete the quests of claiming them and defending them (they will be attacked a few minutes after you claim them). You can sometimes obtain some plans that way and that can be much more use than a couple of fusion cores.