Adding a Texture from Photoshop
Maya 2012 Tutorial
How to Add a Photoshop PSD Texture to Maya Object
Texture maps provide a method of creating "synthetic" geometry. Instead of modeling everything in the scene, may times objects in the back of the scene can be simple geometry with an image applied.
Textures are also helpful when adding non-rectangular objects to the scene such as trees and flowers. The non-object areas can be masked in Photoshop so only the object appears in Maya.
Add a square polygon plane to your scene (Create > Polygon Primitives > Plane). Using the Channel Box, rotate the plane 90 degrees along the x-axis.
In Photoshop, open a new 500 pixel x 500 pixel document. Using the filters, brushes and text create your texture image.
Save the original psd file as a backup, then save a flattened version (Layer > Flatten Image) as a JPG or TIFF file in your project's sourceimages folder. Be sure to remove all guides from this version (View > Clear Guides).
Returning to Maya, right click the plane and choose Assign New Material > Lambert.
With the shader open in the Attribute Editor, click the checker-box next to the color slider. In the Create Render Node box, right-click the File icon and choose Create Texture. This creates a file texture that is UV mapped to the object.
Under the file tab in the Attribute Editor, click the folder next to the Image Name section. Navigate to the sourceimages folder and choose the texture file. Render your image.