Why do most other languages have masculine and femenine words and English doesn't? And why are they there in the first place?

To differentiate between masculine and feminine of course. German has a third 'gender', the neuter: der, die, das. In these cases the adjective adjusts to match the gender of the noun. Yes, it would be a lot easier if, en français, I didn't need to know that a computer is masculine and a computer mouse is feminine. I do not know the history behind this.

Here's more reading for you: Grammatical gender - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Grammatical_gender)