Ik zal Anna morgen opbellen.

I will call Anna tomorrow.

Breakdown of Ik zal Anna morgen opbellen.

• ik: I
• Anna: Anna
• morgen: tomorrow
• zullen: will
• opbellen: to call up

Questions & Answers about Ik zal Anna morgen opbellen.

What does zal mean in Ik zal Anna morgen opbellen, and do I always need it to talk about the future?

Zal is the Dutch auxiliary verb used to form the future tense, equivalent to English will. It tells you that the action (calling Anna) will happen in the future. However, Dutch often uses the present tense for planned or near-future events. So you can drop zal and say:
Ik bel Anna morgen op.
This is perfectly natural and conveys the same idea for something you intend to do soon.

Why is opbellen split into bel ... op at the end of the sentence?

Opbellen is a separable verb (a verb plus a prefix). In the infinitive it’s written as one word, but in a main clause the prefix op detaches and moves to the end. The finite verb (here zal) stays in second position, and the infinitive bellen stays near it, while op goes to the very end:
Subject – finite verb – object/adverbials – non-finite verb – prefix
Ik (Subject) – zal (Finite verb) – Anna morgen (object/time) – bellen (infinitive) – op (prefix).

Can morgen be placed somewhere else in the sentence?

Yes. Morgen is an adverbial of time and fairly flexible. Acceptable alternatives include:
Fronting: Morgen bel ik Anna op.
Mid-field variant: Ik bel morgen Anna op.
Dropping zal: Ik bel Anna morgen op.
Just avoid placing morgen after the separable prefix (…op morgen) – that sounds odd.

Why isn’t there a preposition before Anna? Is she an indirect object?

No preposition is needed because Anna is the direct object of opbellen. In Dutch, people you call are objects of the verb, not indirect objects, so you simply use the accusative form without aan or any other preposition.

How would I make the sentence negative? Where does niet go?

Place niet before the separated infinitive (+ prefix). With zal it becomes:
Ik zal Anna morgen niet opbellen.
If you drop zal and use the present tense, you still put niet before op:
Ik bel Anna morgen niet op.

How do I replace Anna with a pronoun?

Use the object pronoun haar (her). You’d say either:
Ik zal haar morgen opbellen.
or with present-tense future:
Ik bel haar morgen op.

How do I form a yes/no question from Ik zal Anna morgen opbellen?

Invert the subject and the finite verb. The verb zal moves to first position:
Zal ik Anna morgen opbellen?
The rest of the elements keep their order in the mid-field.