The high-pass (or if you prefer low-cut) filter has a programmable cutoff frequency. It effectively removes frequency components below a selected cutoff frequency from your sound file. This is useful to remove rumble and power line noise.
The low-pass (or if you prefer high-cut) filter also has a programmable cutoff frequency. It effectively removes frequency components above a selected frequency from your sound file. This is useful to remove hiss.
Use these filters only when needed and if you know precisely what you are doing. This is going to affect your digitized files. If Nyquist or aliasing mean nothing to you, you should probably not touch these functions. Always test filtering and other effects you apply to sound files before you get rid of the valuable originals.
There is NO need to use these filters when you do sample rate conversions as Vox Studio applies anti-aliasing filters automatically and transparently.