Modeling takes patience and dedication to many small details, so if you find tutorials impossible to follow through you should probably quit trying to model for now. Or, you can continue trying and become master modeler one day. The key here is love, which gives you strength to learn and do all the boring stuff, without love and desire to see results of your modeling nothing will happen.
Re-skinning however is much easier, so you can start from there.
1) use OpenBRF to find texture name of some model. For your first try, I suggest starting with some simple model in shape of the box.
Material is composed of one or more textures,
for example Austrian cuirassier model material uses texture called austrian_cuirassier.dds (which is main texture with colors),
and a texture called Austrian_cuirassier_n.dds - textures that end with "_n" are called normalmaps,
normalmaps are textures in shades of purple/pink which hold the data of depth, and it's purpose is to make texture seem more like 3D than a 2D image painted on a model, by making some realistic shading. Darker parts of normalmap texture will make it seem that part of texture goes deeper towards model center, while brighter parts will make that part of image seem to stick out. Normalmaps are actually more complex than explained here, but this is all you need to know for now.
2) after you chose main texture you wish to edit, open it in Gimp, it is free program which is able to open .dds images and export them as .dds files.
3) take a brush, and paint something over the texture, then export it as .dds image with different name (due to some bugs in OpenBRF I can't guarantee just replacing texture inside material will work right away, so its best to create new .dds file, and a new material along with it). While exporting choose "generate mipmaps" option, which is important if you want your texture to look decent from distance. I can't recall best compression settings to use for M&B textures, search forums for that info.
Btw, you should export image into YourMod/Textures/ folder of course, because that's where textures should be.
4) open OpenBRF, import your new texture and create new material along the way
5) if you didn't change basic texture too drastically, then you can use it's default normalmap as well, by adding existing "_n" texture as material's normalmap.
6) select model for which you changed texture, and instead of it's default material enter your new material name. Changes should be visible from preview window right away, if show texture is on.
7) learn how to use gimp plugins or other tricks to generate your own normalmaps for your textures.
