It depends on the thing that belongs to us.
La nostra caramella - our candy/sweet. (singular feminine noun)
Le nostre caramelle -our sweets/candies. (plural feminine noun)
Il nostro cane - our dog (singular masculine noun)
I nostri cani - our dogs. (plural masculine noun)
1) when you need the infinitive 'to drink' (it's a little irregular, bere not bevere as you might think)
2) No, because you can only have one conjugated verb, after that come the infinitives or (if you're using avere or essere possibly the participles).
If it helps think of può as 'he/she/it is able' then tack on the 'to drink'