Dig a trench that slopes gently downhill, usually a fall of about 1 in 100, so roughly 10mm of drop for every metre. Line it with geotextile fabric to keep soil out, add a bed of gravel, lay a slotted or perforated agricultural pipe (in Australia this is commonly called 'ag pipe'), cover it with more gravel and fold the fabric over the top. Surface water and groundwater filter down through the gravel, the perforations let it into the pipe, and the slope carries it to a discharge point, a stormwater pit, a soak well or daylight at a lower part of the block.
The gravel creates void space so water can move freely and the pipe doesn't silt up. The geotextile fabric is the part people skip and regret, without it, fine clay and silt wash into the gravel over a few seasons, clog the voids and the drain slowly stops working. In Australian clay soils, particularly across western Sydney and parts of Melbourne, fabric isn't optional.
A French drain has to discharge somewhere legal and sensible. Common outlets are the council stormwater connection, a soak well or rubble pit on a free-draining block, or simply 'to daylight' where the land falls away. You can't legally dump stormwater onto a neighbour's property, so on a flat block the discharge point is often the part that needs the most thought.