Der Beitrag wird erst sichtbar, wenn die Redaktion ihn bestätigt hat.

• wird sichtbar is a passive‐style construction (Zustandspassiv) using werden
  • adjective to express “becomes visible.”
• ist sichtbar would merely state the condition “is visible” without highlighting the moment of appearance.
• There’s no active verb like zeigen because the focus is on the post’s change of state, not on who makes it visible.

• erst here means “only” or “not until.”
• It indicates that the post will not become visible before the editorial team confirms it.
• Natural translation: “The post will only become visible once the editors have approved it.”

• wenn is a subordinating conjunction, so German grammar pushes the conjugated verb to the very end of that clause.
• In subordinate clauses (introduced by wenn, nachdem, obwohl, etc.), the finite verb (here hat) must follow all other elements.

• wenn is used for conditions or for events in the present/future (“when/if”).
• als applies only to single past events and wouldn’t fit a future/conditional meaning.
• sobald means “as soon as” and stresses immediate succession; you could say:
  Sobald die Redaktion ihn bestätigt hat, wird der Beitrag sichtbar.
  but wenn here underlines the conditional “once/if” aspect rather than “immediately upon.”

• ihn is the accusative masculine singular pronoun referring back to Der Beitrag.
• Since Der Beitrag (der Beitrag) is masculine and is the direct object of bestätigen, we use ihn.

• Redaktion denotes the editorial team or office responsible for reviewing content (e.g., a newspaper’s or website’s editors).
• In English, you might say “the editorial team,” “the editors,” or “the editorial office.”

Here are two options:
1) Split into two clauses:
Die Redaktion bestätigt den Beitrag, dann wird er sichtbar.
2) Use sichtbar machen (“to make visible”):
Die Redaktion macht den Beitrag erst sichtbar, wenn sie ihn bestätigt hat.