Left means big goverment and right means small government in a basic sense. So a left wing party would run a welfare state and nationalise the utilities and railways, say, and a right wing one would be more into privatisation (as the Tories did in the 80s) and personal responsibility e.g. fewer state benefits.
Tories are centre right and the other two main parties float around the centre.
It's not as straightforward as left and right though. Political Compass explains it quite well and you can take a test and see where on the compass you stand compared to people like Hitler and the Dalai Lama (fingers crossed eh!). It explains why political positions lie on a 2D axis not a straight left-right line.