So, you opened Blender and the interface could look like this:
(http://img510.imageshack.us/img510/9751/startingscreen.th.jpg) (http://imageshack.us/photo/my-images/510/startingscreen.jpg/)
The interface is divided in 3 parts (1,2,3), one broad timeline(3) in the bottom, broad 3d window (1) left with Toolbar left(summoned by "T") and Object Properties (summoned by "N"). To the most right, there's Scene Properties (2) with little important buttons down.
If it doesn't look like this, grab and pull at the corners marked by green "1" to get new windows and click on green "2" to select the appropriate window type in menu: that would be "properties", "3d view" and "timeline". To make windows vanish, direct the cursor on the separation lines between windows, until a doublesided arrow appears, rightclick, select "join area" and click on the window you want to disappear.
Now, select the cube with rightclick (it might be already selected, its outlines being yellow) and hit "X" to delete it.
Mind that, the key shotcuts works accordingly with position of the mouse cursor. So if the cursor is elsewhere than the window you work, the shortcut will either won't work or do something else.
Now, you import your model. The ones who already have their model ready and parented/joined all clothes to the mesh, may skip this step until further notice.
Go up left to "File" menu, select Import/Wavefront (.obj) and select your file, wherever it is. Click on Import OBJ. Now this should look like following.
(http://img843.imageshack.us/img843/5382/coordinates.th.jpg) (http://imageshack.us/photo/my-images/843/coordinates.jpg/)
The coordinates are shown by the red arrow. Y is the axis the model is facing, X comes from the side and Z comes from the top.
The imported model is still off - it needs to be
moved (Don't. I did it and messed up the deformation later), but rotated a bit on X axis. It can be done with mouse, but i prefer the shortcuts: it's quicker.
So, switch first from perspective to orthogonal view with Numpad 5, then hit Numpad 3 to the "side view."
(http://img26.imageshack.us/img26/9687/sideviewl.th.jpg) (http://imageshack.us/photo/my-images/26/sideviewl.jpg/)
Numpad 1: front
Numpad 3: side
Numpad 7: from the top
also,
Strg+Numpad 1: from the back. Try the other combinations to figure out.
Read the spoiler if you want to know how the meshes are moved along the axis. Again, don't do it here, the mesh position is fine as it is.
To move the mesh in the middle among the Y axis, hit the following sequence of keys (not combination): "G"->"Y" (grab mesh by the Y axis) and drag it with mouse to the middle.
If you look at the mesh closely, you can notice that it's a bit tilted forward, so you need to rotate it along the X axis so it stands upright.
Now there is a little difference between object and mesh which you should know.
(http://img189.imageshack.us/img189/857/objectsandmeshes.th.jpg) (http://imageshack.us/photo/my-images/189/objectsandmeshes.jpg/)
If you start to rotate the selected object while in Object Mode, it will spin along the object's axis. (the little orange dot left in the middle and not as intended). But we want to rotate only the human mesh IN this object, and a object can contain multiple meshes.
So, select with rightclick the object and hit "Tab" to switch into Edit mode. The mesh must be already glowing yellow, selected, but if it don't you could select and deselect all meshes with "A" (as well as the bones, what comes later)
Hit sequence "R"->"X" and adjust the rotation with the mouse. Mind that, the closer the distance of the mouse cursor to the object is, the faster will the object spin. So to adjust precisely, move a mouse cursor a bit aside, before you hit the sequence.
Hit "Tab" to go to Object mode back.
Now, switch to the front view with Numpad 1
We will now add a new object, a single bone, but first, a short explanation to this thing:
(http://img263.imageshack.us/img263/2288/3dcursor.th.jpg) (http://imageshack.us/photo/my-images/263/3dcursor.jpg/)
This is a 3d cursor and is where the bone or any other object will appear, after you add it.
You can place it wherever you want with left mouseclick, (depends what view you have on) but also snap it to the grid or to the center of the scene, if you summon the Snap menu with Shift+S, if you want to place it precisely.
For example: leftclick just above the pelvis of the mesh, (define height) then switch to side view (Numpad 3) and leftclick again at the same height (define length). It's now directly in the mesh.
Switch back to front view.
Summon the "What-to-add" menu with Shift+A and select Armature/Single bone. Whoops, nothing happened.
Go to those important little buttons i mentioned earlier, at the Scene Properties, in the right. Press one with little stickman on it and find above the X-Ray field. Check it.
(http://img267.imageshack.us/img267/4239/xrayr.th.jpg) (http://imageshack.us/photo/my-images/267/xrayr.jpg/)
Now the bone is clearly visible and fit to work with. Also, the field i marked green, is the appearance, how the bones should be displayed. It matters, especially when we recalculate their rotation and weight them, but that comes later.
Go back to our bone, which is called Armature. It is, as a object, (we're still in Object mode) our whole skeleton. It just needs to be edited.