If you are lucky to have your ancestor's will proved there, then the will, once located, can be ordered online. The records are also on microfilm at the Family Record Centre in London, and large A3 copies can be taken very cheaply.
The PCC covered the majority of southern England and the majority of Wales. These wills cover the dates from 1858 back to 1384. It is worth noting that from the beginning all wills had to be proved in the church or other courts. It was rather an ecclesiastical matter. There were more than 250 of these ecclesiastical courts, making the tracing of ancestors wills and administrations, somewhat of a nightmare. But as time went on the importance of the PCC grew and more and more southern and Welsh wills were proved in this court. Its importance was recognised further when the Bank of England in 1810 ruled it would only accept PCC wills.
But what if your ancestor came from southern England or Wales and you can't find a will on the documents online website? Well, firstly it may be as simple that he just didn't make a will, or he could have had his will proved in one of the other many courts of the land. Records of these courts are normally held in the local county record offices. There is not one whole index to cover them all, but, surprisingly, many are indexed, so all is not lost. Also many are published, too. If you know the county or area your ancestor came from contact the Country Record Office direct,( you can find lists on GENUKI); the majority will be able to answer your request as the wills are mainly indexed and you can obtain a copy for a small charge.
It is important to understand that a will should be found in the court where the probate was granted. Probate means simply the permission that's granted to the executors to go ahead and follow the command of the will. If the person does not leave a will then the next of kin is given what's called "Letters of Administration," which then allow the person to deal with the goods, chattels, and estate that's left. So, firstly, there is a need to know where the will would have been proved and, secondly, where the wills of that particular court are now held.
The Society of Genealogist in Farringdon London has quite a few will indexes. The Society's website is www.sog.org.uk, and it has an online catalogue SOGCAT which you can access from the website.
Also worthwhile is to search the actual library card catalogue at www.familysearch.org, as they too have some indexes. Accessing these indexes would mean a trip to your local Family History Centre at some stage to search the indexes, once you have ascertained they do have the records.