The speaking in tongues part, from what I've learned, is supposed to mean the Holy Spirit is speaking through you, and that we're not meant to understand or interpret the actual words being said. That's if what we're saying has an actual meaning
Plus that part is one of the things (as I was taught) that you do when you feel the Holy Spirit or whatever, like some others are shaking, dancing, crying, and clapping
I don't fully understand it myself