«ь» at the end of a word indicates that the ending is soft. However, those words still have gender cases and, unfortunately, you just have to memorize which words are masculine, and which are feminine. For example:
тетрадь is feminine
словарь is masculine.
I wish there was a trick that could be used to remember which words belong to which gender, but to my knowledge there is no such thing.
As for the друга topic:
друга is masculine, it has just been declined from the nominative case друг into either genative, or accusative (depending on the context).
У моего друга есть футбольный мяч. --- Is in an example of genative case declination of друг
Она любит своего друга. --- Is in an example of accusative case declination of друг
Человек
Человек can mean either man or woman (person), but many times is often regarding a man, from what I know. In my class, we usually assosiate Человек with man (person - if we are unsure of the context), and usually address women as женщина.
I hope that I have helped some.