What you say here is like saying your car batter is dead, so how do I change the oil?
A french drain is intended to remove surface water from your property.
However, if you have a wet basement, there are a number of issues which could be causing your problem.
First of all, my favorite, where are your gutters draining to? Hopefully, they are either tied to a storm drain or drywell, or, they are directed to splash blocks which force the water away from your foundation.
Second, the ground should slope AWAY from the home for at least 10'. This includes landscaping, so no cute little garden berms that trap water between the berm and the foundation.
Third, your basement wall may just need a petroleum based sealant applied to the outside of the foundation ($$$)
Lastly, the kind of drain you are looking for is called a curtain drain. These run around the property you are trying to keep firm, and are intended for areas with extremely high water tables. Essentially, a curtain drain forms a "curtain" that sheilds out the groundwater and forms an island of dry land. The drain is created by digging a trench as deep as your basement, placing 1" or larger ROUND rock in the bottom, followed by one or more layers of 6" perforated pipe and more 1" rock. There is debate about filter fabric which I will leave to other professionals, but this drain is then tied to a downhill storm drain, or terminates "downstream" from the flow of groundwater in a way that it doesn't seep back to the house.
A curtain drain should be installed by a professional with a big boy backhoe, and you must make sure you have all of your utilites located first, so you don't hit a gas, or fiber optic line, either of which will cost big bucks.
You need to have some professional consulting on your problem before you start bashing at your property. I can't do it from text alone.