A Sharpie is a very permanent marker, which you need to be careful with. It comes with a variety of tip width and colors, and even is available with a new retracticle tip cover. Sharpies, (or other brands of permanent markers) are useful in lettering posters, marking packages for storage, artwork, or other tasks where a permanent lable or mark is desired.

[edit] Steps

Write Out Loud! Sharpies in neon or brilliant basic colors are highly visible when used on a contrasting surface. An example would be black on white, but the Sharpie's ink doesn't fade or bleed on most surfaces, so you may find that blue on red or purple also gives a very good contrast.
Keep your tip covered. The new Sharpies with a retractible tip are great, since you click the button, and the tip is secured to prevent leaking and/or drying out.
Store the pens with the point up, to help further prevent the possibility of ink leaking.
Understand that permanent marker means just that, the ink is difficult to remove, and will bleed through almost any paint, especially latex wall paints, so never mark on a wall or other surface thinking the ink can be painted over in the future.
Allow the ink to dry for a few seconds on glossy or slick surfaces. It is possible to smear or smudge a Sharpie line on these surfaces if the line is rubbed immediately after it is drawn.
Do not leave a Sharpie in direct sunlight, particularly on the dashboard of a vehicle on a hot summer day.
Buy multipacks for savings if you use very many Sharpies. They are available in 2-packs, 3-packs, 5-packs, and 12 packs, and multicolored packs as well, usually at a lower price per unit than individual pens.
Look at the variety of tips offered, from extra-fine to wide, depending on the width of the line you desire.