Learn Hardcore Norwegian: Kjøpesenteret gir en stor rabatt på datamaskiner i dag. - The shopping mall gives a big discount on computers today.

Gir is the present tense of å gi (to give). In Norwegian you literally “give” a discount. In English we usually translate this as “offer.” You could also use tilbyr (present of å tilby, meaning “to offer”)—for example:
Kjøpesenteret tilbyr en stor rabatt på datamaskiner i dag.
Both are correct, but gi rabatt is the more idiomatic choice in everyday Norwegian.

Why is kjøpesenteret in its definite form?

Kjøpesenter is a neuter noun. To make it definite singular, you add -et:
kjøpesenter + et = kjøpesenteret → the shopping center.
If you wanted the indefinite version (“a shopping center”), you’d say et kjøpesenter.

Why do we say en rabatt and not et rabatt?

The noun rabatt belongs to the common gender (en-gender). Common-gender nouns take en as the indefinite article:
en rabatt = “a discount.”
Neuter nouns would take et (e.g. et hus = “a house”).

Why is the adjective stor not stort before rabatt?

Adjectives agree with the gender and definiteness of the noun. For an indefinite common-gender noun you use the basic form of the adjective:
en stor rabatt.
If it were a neuter noun, you’d add -t: et stort hus. If it were definite, you’d add -e: den store rabatten.

Why is på used before datamaskiner, and what does it express?

In Norwegian you express what a discount applies to with rabatt på noe = discount on something.
på datamaskiner means “on computers.”

Why is i dag placed at the end, and could it go elsewhere?

Time expressions like i dag (“today”) can appear at the beginning or the end of a sentence. Placing it at the end is very common in spoken Norwegian. If you want to emphasize today, you can also start with it:
I dag gir kjøpesenteret en stor rabatt på datamaskiner.

Why is datamaskiner in the plural? How would you say it in the singular?

Datamaskiner is the plural indefinite of datamaskin. The sentence talks about computers in general, so we use the plural.
Singular indefinite: en datamaskin (“a computer”)
Singular definite: datamaskinen (“the computer”)

What’s the difference between a kjøpesenter and a butikk?

A kjøpesenter is a shopping mall—a big complex with many shops. A butikk is a single store or shop. In a kjøpesenter you find several butikker.

Can we omit the article and say kjøpesenteret gir rabatt på datamaskiner i dag instead?

Yes. In ads or headlines you often drop en:
Vi gir rabatt på alt i dag!
Omitting the article makes it more general and punchy. Including en (gir en rabatt) specifies that it’s one big discount.