I've not used that brand, but I assume that it works the same as others. The Moist button adjusts the duration that heat is applied to the sealing element to allow for bags that may be cold and damp with moisture. The idea is that it allows time for the moisture to evaporate before during the seal time.
There is also a gentle function, that simply stops the vacuum pump as soon as there is the slightest resistance against it.
The manual Manual button is for the sealing element. It operates the seal function. Useful if you buy your bag material in rolls.