Do I need to declare income from a side hustle if I’m not making a lot from it? And if I need to pay taxes when and how do I do that?

I'd be making 24k¥ a month in total giving private language lessons on the side (without deducting transportation n such), do I need to file it? And besides that, when and how do I pay taxes for it? All the info I could find was related to filing not paying.