This week's tutorial explains how to install user scripts that increase the functionality of the encyclopedia's interface. Such tools range from rather simple scripts - for example, that replace some text with other text - to complicated behemoths that do everything from fighting vandalism to closing AFCs.
If you are using the Monobook skin (for more on skins, see WP:SKIN), your scripts page would be at this location. In general, if you use skin X, your scripts page would be at User:(your username)/X.js.
Once you have navigated to the page, you should see the following box:
This means that unknowingly putting malicious scripts on your scripts page may lead to your account being compromised. One must always be careful when installing scripts.
A better question would be, "What can't scripts do?" Scripts, as mentioned briefly above, can change Wikipedia's interface in drastic ways, as well as providing semi-automated ways to edit. The latter is particularly useful for vandalism fighting, though it has many diverse applications.
Some of the most well-known scripts are:
Which tools should you install? Consider first which tools you will actually have much use for. If you spend your time voting in XfDs, vandalism reversion scripts may not be useful for you, and vice versa.
If you wish to use the same scripts as another user, there are two methods. One is to simply substitute their script page onto your own. The second is to use the importScript command, which works as follows:
importScript('OTHER USER'S SCRIPT PAGE');
A more recent feature is the "Gadgets" tab in your preferences page. If you want to use a gadget (user script or CSS modification) that is listed, you simply check a box and save your change. The list includes some of the more well-known scripts. (If you want to customize a script, you'll need to install the scripts manually.)