How to cook?

Hi everyone. I have a fairly general question about independent living, which is...

How do I learn to cook?

I'm an adult with Aspergers. My wife is disabled so we have someone come in and cook us a meal each day. I don't know if this will continue indefinitely, so I'd like to learn how to do it. Before my wife was disabled, I would cook the meal, but it would be something simple like a stir-fry ("throw all ingredients into a wok for 5 minutes"), something pre-prepared like those packets of chicken wrapped in bacon in a metal container you just put in the oven, or something simple out of a packet like 10-minute pasta.

My problem is that I follow the instructions on the packet or recipe to the letter. If it says I need 200g of flour, I will measure out 200.00g of flour using digital scales (beause these are far more precise than a waving needle) because I don't know how adding 202g will affect the recipe. If you read any recipe from any recipe book or online, you'll find they're almost all ambiguous in places ("boil the rice until it's cooked" - how do I know when it's cooked? What if I've had to change the amount because someone is coming around for dinner?), and seem to require a long tail of implied knowledge about how cooking works. Someone came 'round once to show me how to cook rice properly, and as he put it on to boil he said "Now just cook it until it's done" and I said "How long will that be?" and he said "Until it's done!". I took down notes but now we have a different hob so I don't know how that changes things. Do you know how many ways of rinsing rice there are on the internet? Some people do it by volume of water, some by time, some by number of rinses. Which is correct? Which is best? Is one way better than the other? What makes them different? How do I know I'm doing it right?

I also find that the instructions on packets are often incorrect. For example, cooking frozen oven chips. The packet says to pre-heat the oven to 200C for fan-assissted ovens (which mine is), which I do and I can tell when it's that temperature because the light next to the temperature knob goes out. It says to put them evenly on a baking tray for 20-22 in the centre of the oven, turning once halfway through. I do this, and after 22 minutes they're mostly-but-not-quite cooked, because the instructions say they should be golden-brown and slightly crispy by then but they're not. After experimentation I just leave them in for 30 minutes then they end up like described - but this isn't what the "experts" have said should happen on the packet, so how do I know (in a general sense, and for other foods) when they're ready? I find it very difficult when packets say "adjust the time accordingly for a fan-assissted oven" or similar - because, how?

I need the instructions to be precise, so I know I'm doing it correctly, and I need them to be correct, but I find this is rarely so. I tried making a pizza last year using a "make your own pizza" packet mix from Tesco, which entailed mixing the flour with water to make the dough - I'd like to say "hilarity ensued" but it was more like "meltdown in the kitchen for an hour" since I couldn't get it right, it was all sticky and un-dough-like and I didn't know how to fix it.

I can cook simple things - meat in a wok is easy because I can visually see and hear when it's cooked (chicken turns from pink to white all over, beef turns from red to brown all over, and the sound changes greatly the moment the juice has all boiled off). But anything else seems utterly beyond me.

So, I think my question is, how do you do things like this? And how do I make this easier? I'd like answers to both please, if you can.

Thanks.