There are 4 visible slots.Default number of materials is 8(max 100).
Starting from left to right:
First 4 buttons: planar,spherical,cubic,cylindrical previewing.
X: Reset material - colors,images.
V: Set(assign) material to selected object(s) or selected mesh face(s).
X: Remove material from selected object(s) or selected mesh face(s).
Transparency:
Used as the transparent color for diffuse image when rendering.
Images:
*Only diffuse image is rendered in views.
*x button will reset image(unload).
*Amount value (0-100%) is used in rendering(image RGB strength).Refraction image can exceed 100%.
Loading:
For each image press the oblong button - <empty> - to bring up the image editor.
*You can copy another material image(if any) instead of loading a new one.
*Animation fields will be enabled if an avi or ifl file is loaded.
Now, press Load.
Select the image and press Open.
<empty> will be replaced with the image's filename.
Copying materials:
A) Right click in a slot and choose the material to copy from.
B) Left click and hold.Move-Drag over a near slot and release left mouse button(pick & drag).