When I try to change the texture on a cube all of the cubes change I am trying to input a texture on blender for one cube for a project. But whenever I try, the entire structure gets changed. In the picture I am only trying to change the color of the cube selected but the entire thing is changing? Any tips? Thanks.
A material is its own data block, and a material can be applied to multiple objects.  So by modifying the material you see the effects everywhere that material is applied.
You must make a copy of the material and apply it to the object you want to change.