help! squirting ??

so.. i’m a 19 year old virgin but i still fuck around with this dude with oral & whatever. I masturbate all the time for years, however i’ve never been able to squirt. one time this guy was fingering me & i squirted & it took me by surprise. I have been trying to do it myself but I only can with him. What am i doing wrong? how can i do it myself?