The systems of compilation for Forex data vary a great deal. There are as many different types of collation as you can reasonably imagine, and some of these methods have been proven over time to be, if not foolproof, then at least incredibly informative. Access to the right data is important in ensuring as high a possibility of success in your trading as you possibly can. This kind of data is freely available, but what information you can glean from it is inevitably limited as it will be full of figures that carry varying levels of relevancy. Raw data is useful only in so far as you can be bothered wading through the masses of information to find only the best predictors.
The data that will be truly useful to a trader is the information produced in a quickly readable form using only the data that is absolutely relevant. This comes in the form of charts and graphs, and this kind of data is available in up-to-date form from any good broker. There are historic Forex charts freely available on the Internet, and these can be used in order to help you understand market patterns. Once you sign up with a broker you will have more recent information, which is absolutely essential for forming a strategy. Your broker will also (usually) give you the chance to have a -practice account- which tests your reading of the data so that any mistakes you make are relatively harmless. In this way you can learn to read the data proactively and safely.