Learn Portuguese (Portugal): Divides o bolo com a rapariga.

In Portuguese, the verb ending tells you who is doing the action. The verb dividir (to share or divide) is a regular -ir verb. The -es ending in divides specifically matches tu (you, informal). Because the ending makes it obvious, the pronoun tu is usually dropped.

Why does divides translate to 'share'? Doesn't it mean 'divide'?

Yes, dividir literally means 'to divide'. However, in Portuguese, it is also the most common way to say 'to share' a physical thing with someone, like splitting a cake or a meal.

I've heard that rapariga can be a bad word. Is it safe to use?

In Portugal, rapariga is the standard, perfectly polite word for 'girl' or 'young woman'. It is only offensive in Brazil, where it is used as bad slang. Since you are learning European Portuguese, it is completely safe and necessary to use!

Do I always need the word a after com?

You need it here because you are saying 'with THE girl' (com a rapariga). The word com means 'with', and a means 'the' for feminine nouns. Unlike prepositions such as de or em which merge with a, com stays as a separate word.