This is not the place for a complete guide (maybe I will look into writing one) but I will give you a few tidbits. First off, like everything in life, prices are usually an indicator of quality. Now there are gems out there that sound amazing and will last but generally if it cost more it will be of higher quality.
The next thing to look into when it comes to a PA system is to determine if you want an active (powered) or non-active (passive) system. In active systems, the amplifier is built into the speaker box whereas with passive systems the amplifier is a seperate piece of equipment. There are pros and cons to both but for most DJs in my opinon, active systems are best for a couple of reasons. All of the hard work of matching the right amp to the speaker and getting the right processing is already done by the manufacturer. As a DJ, you plug the speaker into a power outlet and then plug in the signal from your DJ rig and turn it up. Also, if you are using a controller, you are probably interested in saving space and by having the amp built-in, thats less things to carry around.
Now brands to look at. I would suggest you do your own research but some of the common brands that offer decent to excellent quality include (but not limited to) QSC, JBL, EV, Mackie, Yorkville, Yamaha, and Peavey. Most products from those companies will be pretty good (except the JBL JRX series which is just garbage). There are other brands out there of course that are really good but will probably start to make your wallet hurt from just looking at the prices.
Now as far as watts are concerned. Watts is a measure of how much work electricity can do. Basically the more watts, the more work can be produced. The problem is this can be very misleading to newbies. Just like you can’t measure how good a computer is by just it processor speed or a camera from just megapixels you can’t go by just watts when looking at specs. The other big qualifiers are the sensitivity of the speaker (you should google this topic as its to much for this post) and how the measurements were taken. In the end the best way to see how loud a speaker is is to go and hear it for yourself.
Finally, how to connect your controller to your speakers. Well both the S4 & S2 have balanced audio outputs (google this) which is important. But basically you take the main output of your controller (XLR for the S4 & 1/4″ TRS for the S2) and simply plug it into your active speakers. Its just that simple.
Hope this helped some.
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