Челове́к can refer both to men and women.
In the past, English 'man' also could refer to men and women, so if you're translating into an old-fashioned English, this might work as a translation. Or if you have a context (e.g. in the sentence «Он плохо́й челове́к» you could translate «челове́к» as 'man').
When it is used with some word to indicate possession (e.g. with genitive noun па́рень Ило́ны 'Ilona's boyfriend', with possessive pronoun мой па́рень 'my boyfriend', with possessive adjective Серге́ев па́рень 'Sergei's boyfriend', with «у» to indicate possession у Ве́ры нет па́рня 'Vera doesn't have a boyfriend'), then it's translated 'boyfriend'.
When no possession is implied, it's translated 'guy'.
The same is true for «де́вушка»: it's either 'girl' or 'girlfriend'.