There is no shortage of ways to design your own circuit boards: from the traditional methods with pen, tape and transfers through to modern computer-aided design, it doesn't really matter what your skill level or experience is. Pretty soon, though, you'll come across Gerbers. The go-to standard for digitally-designed printed circuit boards, the Gerber format - RS-274X - contains all the information a manufacturer needs to produce physical circuit boards matching your designs, from each layer's layout to where through-holes and vias should be drilled.
Regardless of the software you use to actually perform the design work, it's near-guaranteed that you'll be asked to export your files to Gerber format before providing them to the manufacturer. Once your design has been Gerberised, though, the work isn't over: you need to be sure that the files that have been generated are correct, and the easiest way to do that is with a visualisation tool - just like the Gerber Viewer recently launched by EasyEDA.
Upload an archive containing your Gerber files - each aspect of the design from drill patterns to silkscreen getting a separate file, all of which need to be bundled together for the visualiser - and EasyEDA's tool will generate images for each layer plus combined images for the top and bottom of the board. As well as providing a guide as to the finished appearance of the PCB - including your choice of solder mask colours - the tool performs various analysis steps which can help ensure that your design doesn't breach any Design For Manufacture (DFM) rules that might prevent it from being manufactured properly.
If you're a Cadsoft Eagle user, there's another new visualisation tool to try: Omniblox by Benjamin Richards and David ten Have takes standard Eagle files - prior to their export to Gerber format - and produces a neat three-dimensional render. While in the early stages, plans are afoot for future upgrades including the ability to render accurately-sized components on top of the circuit.
EasyEDA Gerber Viewer is a viewer for Gerber RS-274X files, Excellon drill files online, After you upload your gerber file, we will render it as images including a top side and a bottom side photo view. At the same time, EasyEDA runs a simple Design For Manufacture (DFM) check, from which you can see the board size, hole and track sizes and clearances of the various PCB objects such as tracks and pads.