This is the 422nd most frequent Icelandic word.
kaupa
"To buy."
In this sentence, 'kaupi' is the first-person singular present indicative form of the verb 'kaupa', used here to express an action currently being performed by the speaker, specifically buying.
Ég kaupi brauð í bakaríinu.
I buy bread at the bakery.
Here, 'keypti' is the third-person singular past indicative form of the verb 'kaupa', denoting an action completed in the past.
Hún keypti nýjan bíl.
She bought a new car.
In this instance, 'kaupa' is in its infinitive form, used in combination with 'ætla' (meaning 'going to') to indicate a planned future action of buying.