Right after, "What guitar should I get?" the next big question is, "What should I get to go with it?" There are big amps, small amps, half stacks, combo amps, modeling amps, and tons of various features on each one. The obvious factors to consider are size and price. Bigger might be louder, but that isn’t always better. Let's look over a few aspects to consider regarding amplifiers.
Obviously the biggest question when purchasing an amp is, "How much I should spend?" A lot of players can get more of an amp for less money by getting a used amp from ebay, craigslist or even the music shop. New amps are really expensive for young musicians. Plus, they are pretty rugged since manufacturers like to make them with the heaviest wood possible (or so it seems). And even if you are hauling it around a lot, your amp is an investment that will last a long time. This is why used amps are a great deal. Make sure you know your price range so that you're not just paying for an amp that says "SRV."
Tube amps are the most popular kind of amp. They are a little more troublesome and fragile, but the tone they produce is the most sought after aspect of amps. Tubes are small glass cylinders that help manipulate the tone of an amp. They sound very warm and overall much better than a solid state amplifier.
Many speakers means a lot of sound. The more you have, the more air you can push without cranking your amp up all the way. With speakers also comes resistance and watts. If you buy a combo amp with the speakers attached to the head, or the knobs and speakers all in one structure, then you won't have to worry about this. However, if you are buying a head and a half stack of speakers, you will want to match up the Ohms and Watts correctly.
Ohms & Watts?
Ohms are a measurement of resistance in electronics. The bigger the speaker, the more difficult it is to power, thus the more ohms. In guitar setups, ohms are usually either 4 or 8, and rarely a 2 or a 16. Each amplifier is capable of using a certain amount of power to make the speakers move; this is called the watts. The more watts, the more power that can be used to push the speakers. However, if an amp is rated at 350 watts at 4 ohms it will be significantly less at 8 ohms. Make sure that you look on the back of your speaker cabinet to see how many watts it can handle at what ohms and pair this number with your amplifier.
If your speaker cabinet can only handle 200 watts at 8 ohms and your amp is pushing 350 watts at 8 ohms, then you can easily overpower your speakers and blow them if you are not careful. The bottom line is to make sure your Amps wattage is LESS than your speaker's handling cababilities.