A Will is a legal document, providing it has been correctly written, signed and dated, with the signature being witnessed by two independent witnesses.
The purpose of a Will is to give instructions as to how your estate (everything you own, including property, money in the bank and personal possessions) will be distributed after your death.
A Will also states who will be responsible to carry out these instructions.
This person, or people, are called Executor or Executrix and have the legal responsibility to ensure that your instructions are complied with, provided that you have left enough assets to pay any debt that you may have.
The immediate priority for most families is to make the funeral arrangements, which is usually done by the next-of-kin or family members working together.
If the next-of-kin is not the Executor or Executrix, it would be helpful to inform the them at an early stage to confirm any recorded wishes or instructions regarding their funeral. If the Executor or Executrix is a Solicitor, they may well be able to help with some of the tasks ahead.
If you have an original Will or a copy, you can open it straight away, there doesn't have to be a formal "Reading of the Will", which may be useful to tell you who the Executor is, whether there are any instructions for the funeral or remembrance or other details which may be relevant.