My wife and I both have accounts with Questrade. There is no minimum amount required, although they charge a fee if your total assets are below $5,000 which most people have much more than that anyway. Investing in ETFs through Questrade is one of the cheapest ways to get into index funds in Canada right now, if you consider both trading fees and MERs.
Basically, you open an RRSP, TFSA or unregistered (margin) account with Questrade (or all three if you like). Transfer in your existing assets from other accounts, or transfer in cash. You then buy ETFs on the stock market (Usually the TSX), just like you would buy a regular stock. An ETF is an index fund that is sold on a stock exchange. Its similar to a mutual fund, but there are some minor differences. Usually ETFs have lower fees than equivalent mutual funds.
If you do sign up with Questrade, feel free to use my referral code which will give me $25 and you between $25 and $250, depending how much you deposit: 495822885388555