A lot of computer circuit boards are configured by jumpers, which act as little on/off or multiple-position switches. Jumpers are used for such things as setting the CPU type and speed, interrupt levels and I/O addresses, and enabling or disabling certain features. In all cases, you should read the manual for the board in question to find out where the jumpers are located and how to use them.
A typical jumper looks like this: , only it's a lot smaller (about ¼" long). Unless you have good size fingernails, you usually will need some tweezers or needle-nose pliers to remove and install jumpers.
A typical jumper block for a simple on/off jumper looks something like this: . To set the jumper in the On position, simply place it over both pins like so: . To set the jumper in the Off position, either remove it completely, or you can place the jumper over one of the pins to keep it handy in case you need to change it later: .
Some jumpers, instead of being on/off switches, are multi-pin switches. Commonly, there would be three pins in a row, and the jumper would cover either pins 1 & 2 or pins 2 & 3 . Note that the position of pin #1 is arbitrary, but will be clearly marked either with the numeral '1' or a box around pin 1.
It's possible that several jumper blocks may be placed adjacent to each other. When this is the case, make sure you know which pins belong to which block so that you don't short-circuit two jumper blocks together. Be sure to read how the jumpers are labeled, as in these examples: .