
mit
with
Expresses accompaniment or togetherness; means 'together with.'
Ich gehe heute Abend mit Freunden ins Kino.
I'm going to the movies with friends this evening.
with
Loading your saved state.

with
Expresses accompaniment or togetherness; means 'together with.'
Ich gehe heute Abend mit Freunden ins Kino.
I'm going to the movies with friends this evening.

by / with
Indicates an instrument, tool, or means with which an action is carried out.
Er fährt jeden Tag mit dem Bus zur Arbeit.
He goes to work by bus every day.

with
Describes a quality, content, or characteristic of something.
Ich trinke meinen Kaffee am liebsten mit viel Milch.
I prefer to drink my coffee with lots of milk.

with
Describes the manner or an accompanying feeling in an action.
Sie erledigte die Aufgabe mit großer Sorgfalt.
She completed the task with great care.

at
Indicates an age or a point in time at which something happens.
Mit 18 Jahren hat sie den Führerschein gemacht.
At 18, she got her driver's license.
The preposition 'mit' always requires the dative. This is a fixed rule that applies to all meanings of 'mit.'
Fährst du mit dem Zug oder mit dem Auto?
Are you going by train or by car?
Pay attention to the context: 'mit' + person usually means accompaniment (together with). 'Mit' + object usually means that the object is being used as a tool or means.
Ich spreche mit meiner Chefin.
I'm speaking with my boss.
When 'mit' indicates a means, tool, or mode of transport, it answers the question 'Womit?' (with what?). This use is very common in everyday life.
Womit hast du das Paket geöffnet? - Mit einer Schere.
What did you open the package with? - With scissors.
The combination 'mit' + noun can describe the manner of an action, similar to an adverb. Typical phrases are 'mit Freude' (with joy), 'mit Geduld' (with patience), or 'mit Absicht' (on purpose).
Er hat mir mit großer Freude geholfen.
He helped me with great joy.
The expression 'mit' + number + 'Jahren' is used to indicate the age at which a person performed a certain action or was in a certain state.
Mit sechs Jahren habe ich gelernt, Fahrrad zu fahren.
At six, I learned to ride a bike.
in
When talking about a journey, mit identifies the vehicle as the means of transportation. In, by contrast, describes where someone is during the journey. So you travel by bus, but sit or stand on the bus.

Mit dem Bus fahren wir nach Köln.
We are traveling to Cologne by bus.
Im Bus nach Köln sitzen wir ganz hinten.
We are sitting at the very back of the bus to Cologne.