Learn French: Il faut apporter son passeport ainsi qu'une photo. - You must bring your passport as well as a photo.

While et simply means 'and', ainsi que translates to 'as well as'. It puts a slight spotlight on the second item (une photo), highlighting it as an important additional requirement. It belongs to the same family of additive conjunctions as non seulement... mais aussi, though it is slightly less emphatic.

The translation says 'your passport', so why does the French use son instead of votre or ton?

Il faut is an impersonal expression meaning 'it is necessary'. Because it does not specify a person, it acts as a general rule ('one must bring one's passport'). In French, the general 'one's' is translated using the third-person singular possessive adjectives son, sa, or ses.

If I wanted to add another action instead of a noun, could I use ainsi que in the same way?

Yes. If you wanted to say 'You must bring your passport as well as sign a form', you could say Il faut apporter son passeport ainsi que signer un formulaire. It seamlessly connects elements of the same grammatical type, whether they are nouns, adjectives, or infinitives.

Could we rewrite this sentence to use non seulement... mais aussi since that is the current lesson topic?

Absolutely. To make the requirement much more emphatic, you could say Il faut apporter non seulement son passeport, mais aussi une photo ('You must bring not only your passport, but also a photo'). The phrase ainsi que is simply a lighter, more everyday way to express addition.