Filter Use???

Sup fellas? What are the use of filters, and how are they used? I’ve heard some talk of having to use 'em for some sachets.

It’s pretty self explanatory, filters are for filtering!
The gear is drawn into a syringe, the needle is removed, a filter gets a needle attached to the outlet , the syringe is attached to the filter and the gear is injected through the filter into a vented, sealed, sterile vial. Voila!