hello,

to the forum!
first of all, what fish do you have in your tank and what size is the tank? Guppies should be kept at a male to female ratio of 2:1.
When your females are ready to give birth they will probably try to hid in the plants, behind the filter or heater, and in other places. They will breathe really fast and they will probably stay still although some will move around and swim as they give birth. Tbh, they shouldn't be in the tank at all if any fish are harassing them, as they will probably get really stressed and might die from it.