You need to choose a wide aperture - if you select the AV setting (which gives you control of the aperture) you want to get the lowest number you can. On your lens it will be something like f3.5 of f4, maybe.
You select the number using the dial and the camera will automatically change the shutter speed.
There is a reciprocal relationship between the aperture and shutter speed - when one changes, the other has to change in order to get the same amount of light into the camera.
Watch out, though - if the shutter speed gets too low (say slower than 1/60 of a second) you might get a shaky picture (though your lens has some stabilisation, which will help). Experiment and see.
The depth of focus is altered by other things, such as the distance you are from your subject, and how far they are from the background, but basically in this case you want to consider the lens aperture.
Get yourself a good basic book and you'll find some helpful advice. It's an important thing to know to make the best of your camera.