in, near, while, at, for, etc.
The preposition "bei" is one of the most complicated ones because it is used in many different contexts. We’ll show them now:
It is used to say that one is with a person (at their home)
Hans ist bei Ralf
Hans is with Ralf (at his home)
Die Kiste war bei mir
The box was with me
This means that one is with a professional in their place of business or consultation:
Ich bin beim Arzt / Frisör / Bäcker
I’m at the doctor’s / hair cutter’s / baker’s
to say that one is at work, at the company, organization or activity:
Bist du bei der Arbeit?
Are you at work?
Ich bin bei der Polizei
I’m at the police station
Er war bei der Bundeswehr
He was in the army
Der Rechner war bei Amazon im Angebot
The computer was on sale on Amazon
Mein Auto ist bei der Jahresinspektion
My car is at its annual inspection
Wohnst Du bei der Schule?
Do you live close to the school?
bei means "during" in the sense of time.
Wovon träumst du bei Nacht?
What do you dream during the night?
Wir haben bei dem Festival einige Freunde getroffen
We met some friends during the festival
With the construction "bei" + nominalized verb you can form a type of gerund in German:
Ich bin beim Essen
I am eating (Sort of like: I am at the meal)
NOTE: Given that all the nominalized verbs are neuter and have an article, the structure is always:
bei + dem + verb in the infinitive ➜ because it always contracts, the form is ➜
beim + VERB IN THE INFINITIVE
Ich bin am Essen can also be said
"Bei" is used together with temperatures or numbers
Wasser kocht bei 100º C
Water boils at 100ºC
Wir fangen nicht bei Null an
We didn’t start at zero
Ich beginne beim Anfang
I’m starting at the beginning
Ich bleibe bei meiner Meinung
I’m sticking with my opinion
Bei does not change, just like all the other prepositions.
Words that follow "bei" have to be declined in dative (it always takes dative)
beim is the contraction of (bei + dem)