What is the meaning of heterosexual and bisexual

Hetero-straight
Bisexual-one can have sex with both genders

Breaking it down into the parts, you have:

Hetero: Different or differing.
Bi: Two.
Homo: Same or similar.
Sexual: In this case, either acts involving the genitals or a romantic attachment (or a preference regarding either)

So, putting them together, you have:

Heterosexual: acts, emotions, or preferences for someone with different genitals than yours.
Homosexual: acts, emotions, or preferences for someone with the same genitals as you.
Bisexual: acts, emotions, or preferences that are directed at persons with either similar or differing genitals.