Using your favorite design software
Most graphic design and CAD software allows you to export your design into a DXF format compatible with most waterjet cutting services.
Note that DXF format is a vector file format, as opposed to a raster or pixel based file format. Vector formats allow precise creation of curves, lines and other shapes. Examples of vector based desgin software include Inkscape, Adobe Illustrator and Corel Draw.
Exporting from design software that supports vector drawing to DXF is typically a matter of choosing File | Export from the menu or File | Save As…, and then picking the DXF format.
If you don’t yet have design software
If you are just getting started and don’t yet have CAD or graphics design software, don’t worry. There are many great software packages out there, all of which are free to use and are of professional quality.
1. Free vector based drawing software for Windows, Macintosh, and Linux:
Inkscape (see the note on Inkscape below)
2. Free Computer Aided Design (CAD) software for Windows:
Solid Edge 2D
3. Open source Computer Aided Design (CAD) software for Windows, Linux, and Macintosh:
QCad or Librecad
4. The Big Blue Saw Designer, an online tool for Java-enabled web browsers.