It all starts with an idea. Taking that idea from just a concept to an actual product is what the fashion design process is all about. It is what drives so many students to pursue a career in fashion because of they drive they have to create.
The first step in the fashion design process is the idea. However, before then it takes research into current fashion trends, analyzing them against past ones, predicting how your design will fair against others already out there. It takes review of trend reports published by other fashion industry trade groups and fashion media.
The next step is the brainstorming process. Conceptualize and draw out the idea onto paper. Experiment with different methods, fabrics, and designs. Not all designers put ideas onto actual paper, however. Many sketch their ideas digitally through computer-aided design (CAD) programs. CAD programs allow designers to test out designs on virtual models, shortening the process a great deal, allowing them to play around more so than what would be possible with paper and pencil designs.
Once an idea is put onto paper, designers then produce a prototype, working with mannequins and eventually models to see how the design will look on an actual person, making adjustments as needed.
Once adjustments are made, designers produce samples of the product with the actual materials that will be used in the mass production of the design. Samples are sent to fashion editors or tested at trade or fashion shows to see how they will be received in the general public.
This entire design process takes an average of six to eight months from initial design to final product. Technology has cut down the time this process took in past years enormously. Through the use of the Internet, fashion designers can reach markets outside of their normal reach, beyond the storefront.
U.S. Bureau of Labor Statistics: http://www.bls.gov/ooh/arts-and-design/fashion-designers.htm