My father in law died a couple of weeks ago and my dp and I had to come back early from holiday to help his mum sort things out. We'd never had to do this before so know just what you're going through.
You can google and find some helpful step by step guides that are really useful. The main things for us to know were:
get a death certificate from the doctor
register the death within 5 days. If you don't know where to go then google - it might be your local town hall, but sometimes it's a different set of offices. Get multiple copies of the certificates as they'll be needed and are cheaper to buy at the time.
phone an undertaker and make an appointment for them to come to the house. They'll help you to plan the funeral.
You are likely to need to contact:
town hall (council tax)
tax and pensions
utility companies
bank and/or building society
life insurance
land registry (to transfer ownership of the deceased person's house)
Some of these will need a copy of the death certificate (photocopies not usually acceptable). Some will just want the number.
Is there a will?
You might need to apply for probate, but that depends on how much is left and how complicated the will is. For us it was simple as dp's dad owned the house jointly so it automatically went to dp's mum and dp's dad didn't have any other assets. That meant we didn't need probate or a solicitor. You can google online to find the probate form and that will tell you if you need to apply.
You may be entitled to claim towards funeral costs. Again, this is something you can check online.
Hope this helps