Okay I don't know what I'm doing at all but I have a surround sound system and the speaker wires are too short so I went to best buy and bought some speaker wire(the kind I bought is ALOT thicker than what came with the speakers) I have a wire splitter(that I can't figure out how to use) and I don't know what to do at all. I know I have to buy some kind of wire connectors(crimp butt connectors or something). But again I've never messed with this kind of stuff before and I wouldn't be if the wires that came with the system weren't so darn short.

if it's just a HTiB, just a twist of the wire and some tape (maybe a dab of solder) will suffice, there's never any more than 15w going through there anyways. If it's an AVR, i would try to replace the run entirely or match the wire size. LOTS more power come from an AVR (30-80w depending on the amp) and mismatched wire sizes might cause issues.

butt connectors

There are videos on Youtube on how to splice wire using a little solder and shrink wrap. If this is going to be a permanent fix, soldering the wires is recommended otherwise twisted connections can come loose or oxidize and you will have problems.

You need to keep the polarity intact. That is the + to + and - to -. Almost all wire has some form of identification from a painted stripe to a small moulded ridge on one of the two wires.

In a 2 channel stereo system, a speaker out of phase causes reduced bass. In a 5.1 system an out of phase speaker, especially in the surround channels, can wreak havoc as many sound effects rely on proper phasing to work properly. If however you do by chance get it wrong, it won't do any damage to your equipment.

All in all, the best fix is to replace the entire wire run. Don't buy the wire at Best Buy either. Go to Home Depot or Lowes. Expensive wire is a scam - read this: http://www.roger-russell.com/wire/wire.htm