Hello & Welcome Installing the RIGHT muffler can improve your car's performance by reducing the back pressure in the exhaust system and allowing better flow, but installing an incorrect one that has too little back pressure can reduce your performance. For example, installing those generic straight through cannon type mufflers that you tend to see alot of won't necessarily be good. Do your research, speak to different exhaust specialists and don't purchase the first one you find. Air filter/Air Panel Filter, same thing. When you read people state they've installed a K&N, BMC, Toms, TRD, Green Stuff, etc replacement filter or panel filter, it means they've replaced the standard air filter ( In the stock airbox ) with a better flowing Cotton Gauze or foam type filter, which gives better air flow and a very slight increase in power. K&N and BMC are generally the best. Most CAI's come with a filter already, generally you don't need to change it, but a few people do, it's just personal preference and some filters have been shown to be better than others. ITG and K&N extreme have shown best results. ECU - Engine Control Unit or simply chip means that you upgrade the engine's management computer. Most of the time manufacturers program the engine management with very conservative settings to safeguard themselves. You can increase the engines performance by having a less conservative tune and optimise the engines settings for better performance. Because you take your other modifications into consideration when tuning all the settings, it's best to do this as one of the last mods.