french drain ????

how deep do i install french drains and what kind of pipe do I use does the holes in perforated pie face up or down

A french drain is usually made up of stone or gravel in a ditch that redirects water (no pipe). If you want to use a pipe in the ditch make sure the perforations are up to collect the water and the smooth side is down to drain the water away.
Also make sure you use stone to stop dirt from entering the perforations. You can also use a pipe that id perforated that also has a sock on the outside.
When digging your trench make sure you dig it with a slope usually it is one foot drop for every 100 feet i.e: if your run is 50 feet it should be 6" lower at the end of the run.

I need to replace a damaged(someone put a fence post through it) French drain and have been reading everything I can find on the subject.

Everything I have read says put the holes down so that water comes in from the bottom. The idea is the trench fills and forces the water into the pipe. Also, assuming the pipe is in a gravel base, it is less likely to clog with the holes facing down.

As far as depth, 24" deep, 6" wide, gravel filled to withing 1" of the top assuming you are putting soil and grass on top.

To clarify, I have not done this yet and am no expert. This info is based on what I have read in a couple books and on the Internet.

I would love any advice that they experts on this forum can provide. I have learned more about plumbing on this forum than anywhere else and have saved thousands of dollars in the process.