A Forex Demo account is basically a trading account that allows you to trade like normal but with "Play Money" It is a great way to try out your Expert Advisors or trading strategies before you put in your own hard earned cash.

You don't actually have to convert a .mq4 file to its .ex4 equivalent as this is done automatically through your MetaTrader platform. Simply paste your .mq4 files into the indicator file within your MT4 installation. Usually this is c:\Program Files/(name of broker)/experts/indicators/ Once done simply start up your Meta Trader or restart it if you already have it open. When Metatrader starts it automatically looks in this folder and converts all .mq4 files into .ex4 ready for using.

MQ4 is the source code of an Indicator or expert advisor. This is the code you could alter (if you know mq4 coding) to change the desired affect of the actual indicator. The .EX4 is the same indicator but it has been compiled so that it will load up and work within MetaTrader. This also can protect the intellectual property of the writer if they do not want it altered at all.