The packaging has instructions, which are very simple. Mix the concentrate (usually a teaspoon or a tablespoon) into your liquid of choice (hot water, cold water, milk, or a mixture; usually 6 to 8 fluid ounces. Six fluid ounces is 3/4 cup). Stir more than you think you need to. Then add flavorings, syrups, cream, or sugar to taste. You can add a bit more concentrate, but this will increase caffeine levels, and a little goes a very long way.
Coffee concentrates can also be used to lend coffee flavor to other foods and beverages. Try mixing a little in your vanilla protein shake or ice cream sundae for a caffeinated kick.