I'm sorry to hear of your loss. It's hard to lose someone you love, then have to deal with everything.
Firstly, it depends on where your grandad was when he died. Was he at home or in hospital? Will there be a postmortem? You will need to register the death, but this can't be done until you have a confirmation of death from doctor - you will usually be given a form and an appointment to go to register his death at the births deaths and marraiges place. When you go to do this, it's helpful to get a number of copies of the death certificate as they will be needed for several things. You can also get some photocopies, but most places require an original death cert.
When you go to register his death, there will be a couple of forms in the pack they give you. One will be for the undertaker - you give this to them and they can then start making arrangements. Another will be for the Department of Work and Pensions, to cancel his pension ect.
When you take this in to them, you can pick up a form for funeral expenses, if you need to claim them. Also, if you were your grandads carer, you need to inform carers allowance of his death, but they will keep paying carers to you for approx 8-12 weeks after his death. (sorry i can't remember exactly, i did all this with my mum and dh, and think i've blocked lots out)
Did your grandad own his home? I'm not sure what happens if he did, but if he rented from council, and there is to be no sucession of tenancy, you will need to inform them of his death, and they will give you a date when they expect you to hand the keys in - should be about 28 days or so.
I think that's about all, but hopefully there will be someone else along soon.