The most basic thing to learn about any manual functions are as follows:
First, set your SLR on Auto/Program/whatever. Aim it at something normal and press the shutter trigger half-way down so it auto-focuses/meters the light of whatever you're pointing it at (keep it a low-contrast situation for now).
Read the shutter speed/aperture settings that it chose for what you were aiming at.
For example, it might be something like "1/500@f/8" in a daylight situation.
Now, there's a lot you can do with that reading, but the most important thing is: as one number goes up, the other must come down in order to keep the amount of light getting into the camera a constant. (numerically they seem to be going in the same direction, but you probably get what I mean)
Shutter speeds in full-stops are:
1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000... and so on
Apertures in full-stops are:
f/1.4, f/2, f2.8, f/4, f/5.6, f/8, f/11, f/16 ... and so on
<--------lettinglotsoflightin------------------------------lettinglesslightin-------->
You may see the patterns.
So, if you want your depth of field to be shallow (more blurry foreground/background) open up your aperture a two stops from f/8 to f/4.
Since this action opens up the hole in the front of the camera letting more light in (by two units of light, or "stops"), you need to somehow restrict the amount of light coming in by 2 stops through another means so the overall quantity of light hitting the film or CCD is the same.
Speed up your shutter so it lets light in for a shorter amount of time, exactly two stops from 1/500 to 1/2000.
Thus, your original 1/500@f/8 reading and your new 1/2000@f/4 are equal exposures.
The first exposure is a bit slower, so moving objects might be more blurred. Also, the aperture is more closed, making more things in focus (like squinting your eyes).
The second exposure is quicker, potentially better at freezinig moving objects. However, since the aperture is opened up more, the plane of focus will be much more shallow, creating a lot of blurry backgrounds/foregrounds.
This is the basis of pretty much everything you can do with a basic manual camera without manipulating light itself.
Taking a meter reading, and manipulating your exposure by compensating shutter speed for aperture or vice versa to get the desired effect... whether it be everything in focus, or freezing a car in motion, blurring your background, purposely motion-blurring, etc.
There are loads of other tools you can use to do the same things while not having to comprimise any of your settings. If you are shooting at 1/5000@f/4 and you want your aperture to be open by 2 more stops to kill that depth of field, but your shutter speed can't get any faster to make up for the increase in light from doing so, you can put Neutral Density filters on your lens. Putting a 2-stop Neutral Density Filter on your lens will reduce the light coming in by 2 stops without affecting color or focus. Incredibly useful tool when you're shooting via the sun and you know exactly what kind of effect you're going for.
edit:
I was referring to this, which was on the same page and sounds incredibly harsh.The only reason I snapped at it really. I just feel like it's a luxury sports car vs. american muscle car argument. Both mechanically capable and could possibly be equal, while one is more of a hand-engineered piece of artwork which comes with decades of history, service, quality, etc. I had attended a seminar put on by one of the wacky German owners of Leica and I was quite surprised by their technology/quality/etc. Before then, I just thought they were shitty P&Ss. No way in hell it's a "starting camera" for sure, but it has its place in the industry and not just for trendy fucks. I think trendy fucks are more likely to spend $60~$100 on a $15 Holga or Lomo at Urban Outfitters or something.
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