How long after taking oxy does it work?

for a first timer how long after taking 20 mg of oxy will it start to work or i can feel it? will 20 mg get me high the first time? how long does it last? and will people around me know im high? OH and do you just take the pill normally? or do yoh let it dissolvr before you swallow it? or do you crush it? id really appreciate it if whoever answers this Q gets all the questions! (: please and thanks!!