There are a huge variety of records available online. But there are a few things to keep in mind:
No one website has it all – you will need to hunt around
Not everything is online – see the Books & Archives section
Sometimes only the ‘index’ is online – that is a database of limited details and no images
Not all records survive – disinterest, carelessness and accidents means that records were not always kept.
Not all websites are available to everyone – some are only accessible to universities.