they will take all your makeup off and sit you in front of a mirror by a big north facing window
you will shudder at how clearly your wrinkles etc show
they will wrap a hair-dresser-type cape round your neck and swathe you with a series of different fabric swatches
you will gasp at how haggard some make you look and breathe a sigh of relief at others.
they will diagnose what colour you are (spring, deep/clear etc depending on where you go)
they then go through all the swatches for that 'season' and make notes about which suit you best
they might put makeup on you after that, depends where yuou are and what's included
and give you advice on stuff like glasses, jewellery, accessories etc
and give you a little booklet of swatches and info to take away with you
DO NOT be sceptical till you have gone to a shop and tried on actual clothes in recommended colours