SOPA is an acronym for the Stop Online Piracy Act. It's a proposed bill that aims to crack down on copyright infringement by restricting access to sites that host or facilitate the trading of pirated content.
SOPA's main targets are "rogue" overseas sites like torrent hub The Pirate Bay, which are a trove for illegal downloads. Go to the The Pirate Bay, type in any current hit movie or TV show like "Glee," and you'll see links to download full seasons and recent episodes for free.
The reason all of this is bad is because all the producers and film directors are not getting credit and the money they should get.  Think of all the time the movie makers took to make a film then someone comes along and records the film with a cheap device and puts it up for download for free.
The idea behind these bills sounds reasonable. They came about in order to try and snuff out piracy online, as the entertainment industry is obviously not excited that many people are downloading their products without payment or permission. The issue is, however, that it doesn't really matter whether you're in support of piracy, against it, or just don't care. The methods are ineffective.

While SOPA and PIPA have the same goals, and much of the same provisions, they are not identical. The wording of each section is often only slightly different, though the meaning is the same, making these differences meaningless.

There are a number of key differences, however. Unlike SOPA, PIPA lacks a provision that requires search engines (like Google and Bing) to remove a “foreign infringing site” from their indexes. This provision in SOPA is one of the most highly criticized.

PIPA also contains provisions that require greater court intervention to go after an accused website than SOPA does.

So does that mean that if the laws were passed everything on the internet would be censored?  Maybe yes, maybe no. For the most part, critics of these bills are basing their arguments on the potential for abuse — a hypothetical worst-case scenario. In other words, if copyright holders and the US government never exploit the powers granted to them in SOPA/PIPA, no innocent website will be affected. In fact, that is the argument of these bills’ supporters; that law-abiding, US-based websites and companies have nothing at all to worry about. But the critics (which include more than a hundred law experts from places like Stanford and Harvard Law) say that the bills are too broad in their language, making them ripe for abuse. The Electronic Frontier Foundation cites instances in which current copyright laws, like the Digital Millennium Copyright Act (DCMA), have been used by companies to silence speech that they found distasteful.