SL is being a crashy little bitch tonight, so I might as well get to some of this finally.
Work smarter, not harder: download the premapped sphere. I have my own that I did the hard way, with a bit different window set up, but this means you don't have to go through all that! And really, my setup is not much different. One less window on the side (I just have one 3d view and the texture on the side, then the panels at the bottom). But, this gets you what you need, so run with it!
Spheres are the most useful to me. Nine times out of ten, I'm using a sphere to start. Occasionally another shape is better, and for that you will have to prep your own- this tutorial gives you a pretty good rundown on that, just choose a different shape for starters if necessary (remember to prep your seams: it has to be able to unmap into one big flat square, so you need a top, a bottom, and 2 sides. Also keep in mind that it has to be a perfect grid).
In the big window with your rainbow sphere, switch from Object Mode to Sculpt Mode in the dropdown. You may find switching to Solid in the dropdown next to that is more useful, since otherwise you can't really see highs and lows and shadows so well. Hit F9 while hovering over the Panels at the bottom to bring up the Editing Panel, and the third block of things over should have tabs: Multirez, Sculpt, Brush. Hit up the Sculpt tab, and start playing with brushes! I start off by blocking out my basic shape (the wireframe view may even be of use here, so you can see your vertices: where your vertices are counts! Textures will map differently, you'll have different amounts of detail, and you may need to cluster vertices in certain areas and leave others as large expanses to get the detail in the model you need) with grab, draw, and even hopping over to the Edit Mode and grabbing points and shoving them where I want them. First run of my sculpts are usually very rough sketches, just to get everything in vaguely the right vicinity. I go in and clean them up with a lot of the smooth tool, white still flipping back and forth with the others to keep detail. Some things require hopping over to Edit to pull individual vertices where they ought to be. Select with the right mouse button (hold down shift for more than one), then hit G to move them around. I cannot tell you how long it took me to stumble across the right thing to find that.
Watch your poles. Depending on how you're going to map, they may make a huge difference. Because you're starting with a mapped sphere, there are no end points. Look in wireframe to see the fact you've got open circles at each end. This causes some problems. If you're not mapping sphere, these ends are going to do other things, but in that case you know what they'll do, so I'm ignoring it. If mapping sphere however, those ends are going to be somewhat messily filled in, with textures pulled off the other side of the model if the texture is mapped 1x1. I've talked about it before at more length, this is just a reminder- grab the whole line of them, and shrink them down to one point, and work with them that way. I usually do that earlier _and_ later in the modeling, as I generally end up pulling them out of whack when prodding at my shape. Select two vertices next to each other, hit ctrl-E and select Edge Loop Select to highlight the whole circle of them, then S and scale it all down to one little bit. Now you don't have to worry as much about texturing (but keep in mind, if either end is massively different in texture, you're going to end up with the dotbleed you already get on spheres at 1x1 texturing).
Switch brushes in that bottom panel, type and size both, to achieve different effects. There are easy peasy symmetry buttons at the bottom of that too- if your model needs to be symmetrical select what you need- you can do a lot of your modeling with symmetry to get the basic shape, and then take it off to do more detailing on either side as well.
Basic camera controls: Hold down alt and left mouse button rotates. Alt+crtl+left button zooms, alt+shift+left button moves. The scroll wheel does odd things in these modes as well that you may or may not find useful.
At a glance, I think the map you come with is 64x64, which is what you want, so you can even just bake over that and save it off. Once you've got your sculpting all happy (for starting out, try something simple so as to not get frustrated: I have a long line of wacky melty skulls I played around with, only some of which I've bothered to keep, but basic construction is one direction symmetry, poke some holes for eyes, poke a nose hole, and shove around the jaw. I wasn't going for realism, because I knew I couldn't attain it, as well as not really caring to achieve it), hit F10 in the Panels, and press that big Bake button in the Bake tab. Your rainbow image should now look like a different rainbow image, save that off as a tga, and ta-dah! you've got a sculpty!
Of course, make sure you save a new file often during this process so you can go back when you've messed up when trying to make it better and suchlike. I usually have 10 or 20 versions of even reasonably simple things, just in case I need to go back. Once you've got it sculpted, save off your final version, trash the earliers unless they have potential to turn into something else, and then you can move on to some of the evils of texturing. You've already gotten enough of a crash course here in the tools that you should be able to sort of muddle your way through it, I think.