Cooking meat well is the first part of a good steak experience. Letting it rest after removing it from the heat is the second part of the equation. Before you sit down to sink your teeth into your prepped food though, we thought we'd give you a bit of a rundown on the importance of slicing your steak a particular way for optimum tenderness and presentation. We've included a handy video for reference that will explain some of the particulars.
Everyone should read this great article on Food Lab at Serious Eats.
Most cookbooks will tell you the same thing: "Slice thinly against the grain." To the majority of us, that'll sound like another language we don't understand. Slicing against the grain means understanding that muscle fibers in meat are laid out parallel to one another, not that much differently than a piece of wood that you might see. Different cuts of meat will have more prominent fibers. Slicing your meat against the grain is going to facilitate the break down of the muscle fiber and will enhance tenderness.