What type of model is it? Is it organic, like a person or is it mechanical. The reason I ask is that there are a couple ways of going about it.
In Maya 4.5 (don't know which version you have) all shading is done in what is called the "hypershade" view. The button to switch to this view is in the toolbar on the left side of the screen near the bottom. That is were you want to go. From there you can can create your textures or grab textures from external files, etc.
Assuming your model is simple and non-organic (I'm not in the mood to explain how to do UVs) you can get started right away. Right click inside the black area under the "Work Area" tab. Then go to Create - Materials - Lambert. This is just one type of material. There are several with diff attributes (reflectivity, etc) but lambert is a good all around choice. If your attribute editor is open (which it should be) on the right: It should show you all the information pertianing to a selected material. From here you can change the color, transperency, etc. (Play around with everything to get a better idea of how stuff works)
Assuming you'll want to get your textures from files I'll show you how. Left Click on the checkered button to the right of Color on the Attribute Editor. Left Click the File button in the new window. The Attribute Editor's display has changed. Next to "image name" left click the filefolder button to the right. Now browse to your .jpg texture file, select it and click open.
To apply the materials in the Work Area to your model. Simply, select the faces which you want to texture. Right click the texture you wish to apply to the faces in the Work Area and select Apply Material To Selection.
That should get you started with all hope. I know it is a rather general answer, but you had a rather general question. Look online, for tutorials. There are tons of them around. Good luck, and if you have more questions just ask.
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