When you place a trade, you will either buy or sell the particular product you're trading, depending on whether you believe the underlying market price will rise or fall.
Once your trade is placed and the price has moved in your favour beyond the cost of the spread, it will be a profit making trade. Likewise, while it remains between the spread range or outside of it against you, the trade will be a losing trade.
The spread is one of the key costs involved in CFD trading – the tighter the spread is, the better value you're getting as a trader. Note that there are other potential costs to consider, for example in CFD trading some markets involve a commission charge, or a combination of spread and commission.
The spread is the last large number within a price quote.