Tailwind is a fine powder which you should mix with water and then sip little and often.  A general rule to start with is 2 servings per hour (or 1 stickpack) mixed in 500-750ml of water or however much fluid you will usually consume in an hour.  You can then experiment with strengths, for example I use 2 servings in 750ml when training but on race day I’ll use the stronger mix of 2 servings in 500ml as I don’t take as much fluid in.  On a hot day I’ll also drink plain water to satisfy thirst but keep to the guidline of 2 servings (200 calories) per hour.