Yay, I can answer this since I just did it.
You go to Social Services. You ask to apply for a NIN (they ask you why) You tell them because you're working.
They take a bit of information and then a few days later you get a letter saying they've booked you an appointment. Be there or be square.
At the appointment you give more information.
Here's the stuff I needed to bring:
Marriage cert
birth cert
any and all payslips.
letter from employer stating when I started, how much I earn... blah blah blah.
Proof of residence. this can be a council tax bill (which, btw, you should have in your name as well). if you rent, bring your rental agreement. Bring any recent bills you have, even if they're not in your name, they'll be in hubbys name and that might help. You'll have to bring proof of residence for every place you've lived in since you've been in the uk.
ID- this means passport, drivers license anything you have. I even brought my SS card. They loved that.
They do give you a list of what you need to bring. Took me an hour and all she did was fill in an application, made copies, chatted with me then said it'd take 3-4 months to get the number.
You don't need to worry about cancelling the number. It's yours for life, whether you use it or not. Kind of like a SS#.
If you move before you get the card with the number on it, inform the office you applied at about your change of address, they'll send the info to your new address. Better to have it in case you move back than to have someone steal your mail, use your number and generally get you in trouble.
For the time being, use a temporary number. Your work should provide you with one. They're easy to create.
And I totally understand about walking so far to work. My first job was 20 minutes away and it was up this huge steep hill. By the time I finished the job, I was well used to it and actually looked forward to the walk to work. (even in the dark, because it was winter, and the rain, and the snow, it was just so nice to be out and about. woke me up)
Good luck on the job. And welcome back!