Go to the IND pages
www.ind.homeoffice.gov.ukand look for the forms to download. You should start preparing now, since the paperwork for the ILR is actually more comprehensive than that applying for citizenship (although by the time you get to that point, you might also have to take the new citizenship exam). You'll need evidence of work (a letter from your employer); the annual tax receipt form; evidence of bank statements, etc.
Though making an appointment is more expensive, I'd do it since it will save you the hassle of waiting for the post. And then you never know when a personal intervention can help. I had to get mine at Croyden before the appointment system, which was a trip to hell. Then when I got to the agent, I was informed that they weren't giving out ILRs that day and had to come back. Then next day I got to the point where I handed them my passport, and the only empty pages were the "amendments and modifications" ones, and they didn't want to put the stamp there. I explained that the ILR stamp was an amendment and modification, and they finally gave it to me. If I'd done this through the mail, it might have taken months.
The ILR lets you search for work as an equal to any EU citizen; it lets you go on the dole; it lets you stay in the UK indefinitely unless there's a 2 year gap. But it doesn't give you any privileges outside of the UK. You don't have any rights to settle or work in the EU, and I don't believe that it gives you equal consideration for applying for a job that an EU citizen might have.
For all of these things, you have to become a citizen.
The UK takes an ILR procedurally more seriously than citizenship; so this is the big hurdle. Yet, so long as you've kept your nose clean in these years, there won't be any problem. It's just so much paperwork.
so 1) start collecting you paperwork; 2) fill the form out, which you can download; and 3) get an appointment in one of the centers. Good luck!
btw, from experience, when coming back to the UK on the ILR, I always got asked how I got it and if I was still working (both irrelevant). But after the first year here on the ILR, I haven't been asked those questions once, so they might just give up after a set time.
good luck!