If you've ever had to use any kind of IC, chances are you've heard of quite a few package types. IC packages are split into two main groups, through-hole, and surface-mount. Through hole packages are the most popular with hobbyists, because of their ease of use. The leads of these packages go through the PCB to the other side, where they are connected to the circuit with solder.
Surface mount on the other hand, does not go through the PCB. As the name implies, the leads from a surface mount package (often called "SMD"packages) are soldered to the circuit on the surface of the PCB. The benefit of this package type is SMD IC's generally cost less to make, and take up much less space on a circuit board. SMD technology is on almost every consumer electronic device which uses IC's, or even resistors and capacitors and many other parts which come in a surface mount variety. The downside is that SMD devices are much harder to solder, and in many cases they require special equipment to solder them.
Chances are, you're going to be working with through-hole packages more often, so I'll elaborate a little more on them. The most common type you'll encounter is "DIP", which stands for "dual in-line package". There are a few different types of DIP packages, but the concept is pretty much the same. The IC consists of the body, with pins lined up on two sides of the body, as pictured below.
Standard DIP packages are all the same width, but they come in different lengths for different pin counts. DIP packages with a larger number of pins are often in a wider DIP package, where the body width is 0.6", as seen below.
Other flavors of DIP you may see are PDIP and CERDIP. These just tell you what material the package is made of. PDIP is a plastic DIP, while CERDIP is made of a ceramic material.
Besides DIP packages, there are many other miscellanious packages. For example, transistors are commonly found in a TO-92 package.
for Surface mount packages, I recommend you check out http://howto.wikia.com/wiki/Howto_identify_chip_packages. There are many different kinds of surface mount packages to choose from, but I personally try to avoid SMD stuff. I'll stick with my through-hole :)
