I place two separate blocks side by side.  I select a custom texture (texture 1) and the click on block 1 and it colors that block the selected texture.  I then select a second custom texture (texture 2) wanting to color only block 2 with texture 2 but as soon as click on texture 2 the previously selected block (block 1) is textured with texture 2 when it should not be changed.

How do I unselect the first block (block 1) so it retains texture 1 when I texture block 2 with texture 2?

I discovered what I done wrong.  I needed to create a new material for each next texture I wanted to use and then select the texture for the new material I wanted to apply before clicking the next block.