
von
from
Indicates a starting point, whether a place or a person. It means 'coming from' or 'starting from.'
Ich komme gerade von der Arbeit.
I'm just coming from work.
from / of
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from
Indicates a starting point, whether a place or a person. It means 'coming from' or 'starting from.'
Ich komme gerade von der Arbeit.
I'm just coming from work.

by
Used in a passive sentence to name the person or thing that carries out the action.
Der Brief wurde von meiner Schwester geschrieben.
The letter was written by my sister.

of / by
Expresses possession or belonging and is often used in colloquial speech instead of the genitive.
Das ist das Fahrrad von meinem Nachbarn.
That is my neighbor's bicycle.

about
Indicates a topic or content; means 'about' or 'dealing with.'
Er hat die ganze Zeit nur von seinem Urlaub erzählt.
He talked only about his vacation the whole time.

of
Selects one or more elements from a larger group.
Einer von uns muss die Rechnung bezahlen.
One of us has to pay the bill.

from ... to
Indicates the starting and ending point of a period of time or a route.
Das Museum ist von 10 bis 18 Uhr geöffnet.
The museum is open from 10 a.m. to 6 p.m.
The preposition 'von' always requires the dative. Regardless of the meaning of the sentence, the noun after 'von' is in the dative.
Das Geschenk ist von meiner Tante.
The gift is from my aunt.
'Von' contracts with the masculine and neuter article 'dem' to form 'vom.' This short form is very common and is used in both spoken and written language.
Ich komme gerade vom Sport.
I'm just coming from sports.
In a passive sentence, 'von' + dative is used to name the person or institution that actively carries out the action. The question for this is 'Von wem?' (by whom?).
Der Kuchen wurde von meiner Mutter gebacken.
The cake was baked by my mother.
Especially in spoken language, 'von' + dative is often used to express possession or belonging. This construction replaces the more formal genitive, e.g. 'das Auto meines Vaters' (my father's car).
Das ist die Tasche von meiner Freundin.
That is my friend's bag.
'Von' is also used to indicate the creator of a work (e.g. book, music), the designer of a product, or the brand.
Ich lese gerade einen Roman von Thomas Mann.
I'm currently reading a novel by Thomas Mann.
When 'von' indicates a topic, it is often combined with verbs such as 'sprechen' (to speak), 'reden' (to talk), 'erzählen' (to tell), 'handeln' (to be about), or 'träumen' (to dream).
Der Film handelt von einer wahren Geschichte.
The film is about a true story.
The combination 'von ... bis' (from ... to) is used to define a temporal, spatial, or numerical range. 'Von' marks the starting point, and 'bis' marks the ending point.
Ich arbeite von Montag bis Freitag.
I work from Monday to Friday.
with
In „eine Person von 40 Jahren“, von describes the person’s age as a characteristic. Mit 40, on the other hand, indicates the point in time or stage of life when something happens. Use von to describe the person, and mit to specify their age when an event takes place.

Ein Mann von 40 Jahren beginnt heute die Ausbildung.
A 40-year-old man is starting his training today.
Mit 40 Jahren beginnt der Mann heute die Ausbildung.
The man is starting his training today at the age of 40.