De koerier zal de kantoorstoel morgen versturen als de betaling rond is.

The combination zal + infinitive (here zal versturen) is the standard way to express the simple future in Dutch. You take the auxiliary verb zullen in the present tense (zal/zullen) and follow it with the main verb in its infinitive form.
Example in English: will send → zal versturen.

Dutch main-clause word order follows the V2 rule: the finite verb (here zal) is in second position, then you have the rest of the verb group and objects, and time adverbs typically come after the object. The pattern is:
Subject – finite verb – object – time – infinitive.
So:
De koerier (S) zal (V) de kantoorstoel (O) morgen (T) versturen (Inf).

In Dutch subordinate clauses introduced by conjunctions like als (if/when), the finite verb moves to the end. Everything else stays in normal order. So you get:
als (Conj) de betaling (Subject) rond (Adjective) is (Finite verb at the end).

Dutch has two grammatical genders: common (de-words) and neuter (het-words). Both koerier and kantoorstoel are common-gender nouns, so each takes the definite article de:
– de koerier
– de kantoorstoel

– koerier: often a professional courier or messenger service, possibly traveling longer distances.
– bezorger: generally someone who delivers locally (e.g. a pizza or parcel deliverer).
In many contexts they overlap, but koerier can imply a specialized delivery service.

Yes. Both mean “to send” or “to dispatch.”
– versturen is slightly more informal and common in speech.
– verzenden is a bit more formal or used in business/written contexts.
You could also use opsturen in everyday language.

Both are correct:
– bureaustoel literally “desk chair,” very common when referring to the adjustable chairs you use at a desk.
– kantoorstoel “office chair,” emphasizes the office setting.
In practice bureaustoel is slightly more frequent in daily speech.