As John Kormylo pointed out the tikz-pgf manual says about the "0 width" line: Line width: The “thickness” of the line. A width of 0 is the thinnest width renderable on the device. On a high-resolution printer this may become invisible and should be avoided. A good choice is 0.4pt, which is the default.. Web.
Beamer is a powerful and flexible LaTeX class to create great looking presentations. This article outlines the basis steps to making a Beamer slideshow: creating the title page, adding a logo, highlighting important points, making a table of contents and adding effects to the slideshow..