
sich melden
to get in touch
To contact someone, for example by phone call or message.
Melde dich doch mal wieder, wenn du Zeit hast.
Do get in touch again sometime when you have time.
to report / get in touch
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to get in touch
To contact someone, for example by phone call or message.
Melde dich doch mal wieder, wenn du Zeit hast.
Do get in touch again sometime when you have time.

to raise one's hand
To draw attention to oneself in order to speak, often by raising one's hand (e.g. in school).
Wenn du eine Frage hast, musst du dich zuerst melden.
If you have a question, you have to raise your hand first.

to report
To pass on information officially to a responsible person or office.
Sie hat den Diebstahl sofort der Polizei gemeldet.
She reported the theft to the police immediately.

to register / report
To register with an authority or institution, or to make one's presence known.
Nach dem Umzug muss man sich innerhalb von zwei Wochen beim Einwohnermeldeamt melden.
After moving, you have to register with the residents' registration office within two weeks.

to volunteer
To make oneself available voluntarily for a task or service.
Zwei Soldaten haben sich für die gefährliche Mission gemeldet.
Two soldiers volunteered for the dangerous mission.
Most meanings of 'melden' are reflexive ('sich melden'), with the person carrying out the action themselves. The non-reflexive form 'etwas melden' (to report something) always means to pass information on to someone else.
Er meldet sich nie bei mir.
He never gets in touch with me.
The verb 'melden' is often used with prepositions. 'Sich bei jemandem melden' (to get in touch with someone) and 'sich für etwas melden' (to volunteer for something) are common. When you report something, you say 'etwas bei einer Stelle melden' (to report something to an office/authority).
Bitte melde dich bei deiner Ankunft am Empfang.
Please report to reception when you arrive.
When reporting information, you often use both a dative and an accusative complement: You report 'jemandem (Dativ)' (to someone, dative) 'etwas (Akkusativ)' (something, accusative). The accusative object is the information; the dative object is the person or office that receives it.
Der Zeuge meldete dem Polizisten seine Beobachtung.
The witness reported his observation to the police officer.
The phrase 'sich melden' is often used in connection with authorities, e.g. at the 'Einwohnermeldeamt' (residents' registration office) or 'Arbeitsamt' (employment office). It means to appear there in person in order to register.
Alle neuen Studierenden müssen sich bis Freitag im Sekretariat melden.
All new students must report to the office by Friday.
The meaning 'to raise one's hand' is typical in class or in meetings. If someone has a question or wants to say something, he or she must first 'sich melden' (raise their hand).
Der Lehrer fragt, wer die Antwort weiß, und drei Schüler melden sich.
The teacher asks who knows the answer, and three students raise their hands.
to report
Both verbs can express giving information about an incident. Berichten usually emphasizes presenting what happened as a connected account, while melden generally refers to a brief, targeted, and often obligatory notification to a responsible person or office. Use melden when the information is to be passed on officially.

Der Mitarbeiter meldete den Vorfall sofort der zuständigen Stelle.
The employee immediately reported the incident to the responsible office.
Die Mitarbeiterin berichtete ihrem Vorgesetzten ausführlich von dem Vorfall.
The employee gave her supervisor a detailed account of the incident.