mithelfen
to help out
To help together with others on a task or job and contribute to a shared effort.
Wenn alle bei der Vorbereitung mithelfen, sind wir schnell fertig.
If everyone helps out with the preparations, we'll be finished quickly.

to help out
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to help out
To help together with others on a task or job and contribute to a shared effort.
Wenn alle bei der Vorbereitung mithelfen, sind wir schnell fertig.
If everyone helps out with the preparations, we'll be finished quickly.

'Mithelfen' (to help out) is a separable verb. The prefix 'mit-' comes at the end in a main clause. In a subordinate clause and in the infinitive with 'zu', the verb stays together.
Hilfst du heute Abend bei der Party mit?
Are you helping out at the party tonight?
The prefix 'mit-' means 'together with others'. So 'mithelfen' (to help out) always means that you are not helping alone, but taking part in a shared task.
Viele Freiwillige haben nach der Flutkatastrophe mitgeholfen.
Many volunteers helped out after the flood disaster.
To name the task you are helping with, the preposition 'bei' followed by the dative is used very often.
Wer hilft beim Abwasch mit?
Who is helping with the dishes?
to help
'helfen' and 'mithelfen' both mean that you support someone or something. 'helfen' is more general: a person can help alone or directly support another person. 'mithelfen' emphasizes that you are working on a task together with others and contributing your part. Learners may confuse the words because they look very similar in everyday situations. When several people are doing something together, 'mithelfen' often sounds more natural. When only the support itself is important, 'helfen' is enough.

Beim Umzug helfen alle Freunde mit.
All the friends help out with the move.
Kannst du mir kurz beim Tragen der Kisten helfen?
Can you quickly help me carry the boxes?