Orgasms.

Jessie
Hi, 
I'm not really sure what is going on because whenever I masturbate I get a sudden pleasure. Which I just automatically assumed was me having an orgasm, but then apparently the average for 'cumming' is around 7minutes of stimulation and it only takes me around 30 seconds when watching porn at the same time? Is there stages in having an orgasm or am I doing it wrong? Any advice or information would be greatly appreciated. Thanks x