Slings are an important piece of gear if you have a long gun; tactical slings provide added benefits, the main one being that you can keep your weapon easily accessible if you let go of it.
The most common type of tactical sling is called a three-point sling because it uses the gun's two sling mounting points and it also attaches to itself. A typical three-point sling is the one commonly available for the MP5 series, as pictured above. In this case, the sling has a snap hook at one end that attaches to the MP5's front sling mount. The body of the sling forms a loop upward and back down to the rear sling loop (either on the receiver or on the stock, depending on the model), where it passes through back toward the front, and this end of the sling attaches about halfway forward on the main loop (see photos below).
Once installed, simply place your head and shooting arm through the upper loop and adjust the fit until it's comfortable and you can shoulder and aim the gun quickly.
Blackhawk Industries makes a huge variety of high-quality tactical gear; these items can be found in use with many elite law enforcement and military units. Most are similar to the MP5 sling described above, but they employ an elasticized section to keep the main loop under control, instead of having the sling come back and attach to itself. One interesting note is the amount of rigging that goes into putting a tactical sling on a full-stock AR-15 or M-16 type rifle. The only really good mounting point for a tactical sling is the front sight, which isn't ideal since the sling can obscure the front sight. There isn't a good rear mounting point without tying the sling around the butt of the stock, which isn't ideal either. Blackhawk's AR slings have an adjustable rigging that goes over the butt of the stock and provides a top-mounted sling loop. Some of their slings provide rigging to go around the front of the handguards in order to avoid using the front sight; the model shown below has omitted this setup in favor of using the GG&G tactical sling/light mount.
