Hi, I not an expert, but a south facing window is a good idea, they need lots of light but not direct sunlight (if the leaves go from their bright green to a dark green they are not getting enough light). I water mine usually once a week, I completely drench it, let it drain through, and that should do it (dont let it stand in water). Fertilize once a month with an orchid fertilizer. There are different types of orchid so you should probably try to find out which one yours is as they need slightly different care,

Good luck,

Helen.

Thank you Helen ,will give it a try .