einsteigen
to get in/on
To enter a vehicle such as a bus, train, or car.
Bitte schnell einsteigen, der Zug fährt gleich ab!
Please get on quickly, the train is about to leave!

to get in / join
Loading your saved state.
to get in/on
To enter a vehicle such as a bus, train, or car.
Bitte schnell einsteigen, der Zug fährt gleich ab!
Please get on quickly, the train is about to leave!

'Einsteigen' (to get in/on; to join) is a separable verb. The prefix 'ein-' comes at the end in a main clause. In subordinate clauses and in the infinitive with 'zu', the verb stays together.
Er steigt schnell in den Zug ein.
He quickly gets on the train.
The verb 'einsteigen' is almost always used with the preposition 'in' and the accusative. This applies to all meanings, whether it is about vehicles, projects, or topics.
Sie steigt in den Bus ein.
She gets on the bus.
The meaning of 'einsteigen' becomes clear from the noun after the preposition 'in'. Is it a vehicle ('in den Bus' — onto the bus), a company ('in die Firma' — into the company), or a topic ('in die Diskussion' — into the discussion)?
Wir steigen am Hauptbahnhof in den ICE nach Berlin ein.
We get on the ICE to Berlin at the main station.
On public transportation, you often hear the announcement 'Bitte einsteigen!' (Please get on!). This is a shortened form of the imperative and means that passengers should now enter the vehicle.
Der Schaffner rief: „Bitte alle einsteigen, die Türen schließen!“
The conductor called out: 'Everyone please get on, the doors are closing!'
to begin
'beginnen' and 'einsteigen' can both express that you are starting something. 'beginnen' is more general and fits almost all actions, courses, conversations, or pieces of work. 'einsteigen' sounds more figurative: you get into a project, topic, or discussion and then take part. Especially with groups, projects, or new topics, 'einsteigen' sounds more natural. For a clear starting point, 'beginnen' is usually more neutral and more precise.

In der zweiten Woche ist meine Mutter in den Computerkurs eingestiegen.
In the second week, my mother joined the computer course.
Nach der kurzen Pause beginnen wir mit der nächsten Aufgabe.
After the short break, we begin the next task.