Purchase a portfolio book from an office supply store.
Gather the items you want to include in the portfolio, whether a resume, pictures, reviews of your work, letters of recommendation or certificates.
Organize the items in a way that makes sense for your profession. For example, if you're a writer, organize your samples by category or chronologically with a professional resume at the beginning. For a chef, place photos of your creations and the recipes you've created. Decide what works best for your profession.
Put everything together into the portfolio, possibly laminating some items or covering with protective paper.
Display the portfolio on a flat surface with direct lighting above on a clean table or desktop. If you're at an interview, display the portfolio in front of the interviewer to point out specific examples proving you have the essential experience she is looking for. At job fairs, position the portfolio, possibly propped up on a table, for employers to peruse.