Meaning that you fall for both genders.
People who are bisexual can fall for both
girls and boys.
If you're a boy, you can fall for girls and boys,
if you're a girl, you can fall for boys and girls.
Some people might have a preference, like girls might have a preference to fall for boys but can still fall for girls, but a bit less than that they fall for boys, but they can also have a preference for girls and fall less for boys.
Same goes for guys/ boys.
People realize tha they're bisexual quite quickly, though some people might deny it since it comes at a
random time or that they've been straight theire whole life so now it's like it's just a
mistake or maybe a small phase.
And
yes, bisexuality (and all the other sexuality's), can accidentally been taken by a
mistake and can actually be a phase, but if it's been longer than 4 years you should start to realize you're actually bisexual.