How do u throw up on purpose?

I tried sticking the end of a toothbrush to the back of my throat, but i didnt throw up. infact it hurts. im just curious thats all. not like im gonna do it or anything. plus, when ur fat, and u loos a little weight, do u get stretch marks? coz im getting ALOT of em around my inner thigh and at the back of my knee. i measured it n it hasnt changed much. just a little weight on. :L was it there already and just got obvious? :( help...