Learn Hardcore German: Wer Hilfe braucht, bekommt umgehend einen Anruf. - Whoever needs help gets a call immediately.

Because wer introduces a dependent (subordinate) clause—a “free relative” clause meaning “whoever.” In German subordinate clauses, the finite verb goes to the end, so you get Wer Hilfe braucht (verb-final).

What exactly is wer here—an interrogative “who” or something else?

Here wer is an indefinite relative pronoun meaning “whoever.” It takes third-person singular agreement and carries case like any pronoun:

Nominative: wer (subject)
Accusative: wen (direct object)
Dative: wem (indirect object) In this sentence it’s nominative (subject of braucht), hence wer, not wen/wem.

Why is there no explicit subject in the second clause?

The whole first clause (Wer Hilfe braucht) functions as the semantic subject/topic for the main clause. German allows this pattern without repeating a pronoun. If you want to make the subject explicit, you can add a correlating pronoun: Wer Hilfe braucht, der bekommt umgehend einen Anruf.

Is the comma required?

Yes. German requires a comma between a dependent clause and the following main clause: …, bekommt …

Can I say “Wer Hilfe braucht, der bekommt …”? Is there any difference?

Yes, that’s fully correct. Adding der is optional and slightly more explicit/emphatic. Without der the sentence is a bit leaner and equally standard.

Can I rewrite it with wenn and jemand?

Yes: Wenn jemand Hilfe braucht, bekommt er umgehend einen Anruf. This is very natural. The wer-version emphasizes “whoever” as a category; the wenn-version presents it as a condition. Don’t say Wenn Hilfe braucht (that’s missing a subject); if you want “help” as the subject, use the passive: Wenn Hilfe gebraucht wird, …

What case is Hilfe, and why is there no article?

Hilfe is accusative (direct object of brauchen). There’s no article because it’s an indefinite, mass-like noun here—“(some) help.” Adding an article changes the nuance:

Hilfe (no article): general, unspecified help.
die Hilfe: specific help already known.
eine Hilfe exists but usually means “a help/helper/aid” in a more countable sense.

Why is it braucht and not brauchen?

Because wer always takes third-person singular verb agreement, regardless of how many people end up fitting the description. So: wer … braucht / bekommt (not brauchen/bekommen).

What case is einen Anruf, and why einen?

Accusative masculine singular. Anruf is masculine (der Anruf). As the direct object of bekommt, it becomes einen Anruf.

What does umgehend mean, and how formal is it?

Umgehend means “promptly, without delay.” Register: neutral-to-formal, common in business/official contexts. Rough synonyms:

Neutral/colloquial: sofort, gleich
Formal/official: umgehend, unverzüglich
Also common: baldmöglichst, schnellstmöglich (a bit bureaucratic).

Where can umgehend go in the sentence? Could it be before the noun?

As an adverb, it typically comes after the verb and before the object: … bekommt umgehend einen Anruf. You can front it for emphasis: Umgehend bekommt …
Attributive use before a noun is also idiomatic in formal styles: einen umgehenden Anruf, umgehende Antwort. Both adverbial and attributive placements are possible, with a slight stylistic difference.

Could I use a verb like anrufen instead of “get a call”?

Absolutely:

Passive: Wer Hilfe braucht, wird umgehend angerufen.
With impersonal man: Wer Hilfe braucht, den ruft man umgehend an. (Note the separable verb: anrufen → ruft … an.)
With an explicit subject: Wer Hilfe braucht, wir rufen umgehend an. (e.g., in a company message.)

How would I negate this?

Two common ways, depending on what you want to negate:

No help needed: Wer keine Hilfe braucht, bekommt keinen Anruf. (Use kein to negate the nouns Hilfe/Anruf.)
Not immediately (but maybe later): Wer Hilfe braucht, bekommt nicht umgehend einen Anruf. (nicht negates the adverb umgehend.)

Why present tense when the call is in the (near) future?

German routinely uses the present for scheduled/near-future events when context makes the timing clear. … bekommt … already implies “will receive” soon. You could also say … wird umgehend einen Anruf bekommen/erhalten, but it’s not necessary.

Could I swap bekommt for other verbs like erhält or kriegt?

Yes:

bekommt: neutral, very common.
erhält: more formal.
kriegt: colloquial. All three work here: … bekommt/erhält/kriegt umgehend einen Anruf.