How much protein should I drink after my workout?

I work out once a day for only an hour (for now). I run for about 30 minutes and then do and thigh exercises for the rest of the time. I'm not very good at balancing meals or whatnot. I bought some Whey protein from GNC and was wondering how many grams I should drink after my workout to help build some muscle. My legs have been getting scrawny! Thanks a lot in advance. :)