Registers may have been written in Latin up to 1730s and will almost certainly be in Secretary Hand.
Documents will almost always contain abbreviations and be written as spoken -emphasising all the letters

The technology of writing

Handwriting - Online course

Palaeography from A2A

Letter examples

Old Handwriting - Help someone!

Double-dating

Latin to English

Latin names

.

Parish registers were introduced into England and Wales in 1538.  
Baptisms, marriages and burials  were  entered onto loose sheets of paper.
In 1597/8 it was ordered that all the older entries be copied into a book of parchement, but often only a minimum was copied and then only from the start of Elizabeth I reign (1558).
It was also ordered that copies of the register should be sent to the Bishop's office - Bishop's transcripts (BTs).   (But who provided the expensive parchement and paid the postage?)
BTs shuffled to a close in the 1870s but Broadwater in Sussex carried on until 1936.
Where the original register has been lost the BT can provide the only evidence of an event.
Also look out for parish notebooks that may have survived.  If you were the parish clerk how would you record baptisms on the day?
1604, the Church of England only recognised marriages by banns or licence.
During the interregnum (end of civil war to accession of Charles II, 1653 - 1660) there was an attempt at registration of births, marriages and deaths - not a success, and many events went unrecorded.
1753 saw another attempt at civil registration.
In 1754  Hardwicke's Marriage Act came into effect using  a standard form of entry for marriage.  Quakers and Jews were allowed their own ceremonies.
From 1 January 1813 baptism and burial entries were standardised in a standard register although many parishes used standardised registers before it became compulsory.
Most registers, once they are full, have been deposited at local Record Offices. 
Non-conformist registers before 1837 were deposited at the PRO (Public Record Office).

Family Search of The Church of Jesus Christ of Latter-day Saints.
Select search   to access indexes to 600 million records, baptisms, marriages and burials world wide on the International Genealogical Index (IGI), formerly CFI

IGI batch numbers 
Search by county, then parish.

IGI middle name index

IGI Codes 
What the prefixes to the batch numbers mean.

LDS centres .  Microfilms/fiche can be ordered for viewing at local (Crawley, Worthing) LDS centres.

Boyd's Marriage Index (1538-1840) is an online version of the printed index at the Society of Genealogists.

Copies of Parish Registers have been made since at least the beginning of the C20 with an acceleration in the last 20 years. 
Copies may be printed, typescript, on microfilm or microfiche.
The Church of Jesus Christ of Latter-day Saints (Mormons) have microfilmed an enormous number  of original registers and provided an index that runs up to about 1870.  Primarily baptisms, but many marriages and burials.

IGI, British Vital records, IGI online??
There is now a continuous update to IGI online, but it still omits records that were there prior to the big update a year or so ago. The fiche version, though very old, includes records that are not on the on-line edition.
The Vital Records are a separate series that includes some duplication of the IGI but is mainly an addition to it. Why they are not on-line is down to the Church of LDS
But why don't they make corrections?
 

Parish register transcripts  are available  at some Public Libraries - Familia

Parish Register copies at the Society of Genealogists

Parish Registers at WSRO

FFHS Books (GENfair)

Parish Register Transcription Society

UK Genealogy transcripts

The institute of Heraldic and Genealogical Studies

Wills

Where might there be a will?

Wills and other probate records
HRO, Winchester