Please keep in mind that you have a home theater receiver. It is old. You may have gotten it 8 years ago, but the connections on it indicate that it may be well over 20 years old in design, or was a very dated design when it was released. It is designed for surround sound playback in a home theater. Repeat it over and over... It was designed for surround sound playback in a home theater.
If you want to play around like a DJ, then this product will be far less than ideal, but can work if you are very careful about keeping volume down.
A mixing board, like you will find in use by DJs is to mix audio from multiple sources into a single output to playback audio. It does exactly what it sounds like, it mixes audio from various sources. It may have other internal features, but typically the main idea is that it will take multiple audio tracks and mix them together with instruments and other live sounds. Some DJs use records for mixing and a mixing board, this is fine if this is what you want to get into. If you want to try mixing music, not from a live sound, then there are tons of mixing programs you can just use on your computer.
You have a LOT of research to do. I would watch a lot of videos on YouTube to learn about all of this before you spend one more penny on any of it. At this point, you have a lot of very entry level gear. It's not expensive, and was never considered good, but it is a good starting point.
Your system is NOT capable of high volume playback, it is the wrong gear for it. So, if you want a lot of volume, you need completely different gear. Actual club speakers with an internal amplifier designed for high volume playback are one option to consider if that's where you want to go. Adding a quality subwoofer is also no small task as they aren't a cheap option.
Keep in mind that nightclubs spends tens of thousands of dollars on their gear. If you have $200, you aren't going to get there from here. Be realistic about what you can expect from what you currently have, and be realistic about how much it will cost you to get better sound.