verb
influence, affect
B1
Means: to influence or affect someone/something. It's a transitive verb: one 'beeinflusst' a person or factor (jemanden/eine Meinung beeinflussen). To indicate source, German often uses 'durch' or 'von' in passive ('von etwas beeinflusst'). Auxiliary: haben. Regular weak verb (beeinflusst). Not reflexive.
Examples
Das schlechte Wetter beeinflusst meine Stimmung.
The bad weather affects my mood.
Seine Meinung beeinflusste die Entscheidung.
His opinion influenced the decision.
Er versuchte, die Entscheidung der Firma zu beeinflussen.
He tried to influence the company's decision.
Details
Mnemonics
picture a line of dominoes where one small push 'influences' the rest to fall; prefix 'be-' covers the whole chain
sounds like 'be in fluence' — imagine 'be in' + 'fluence' (influence)
Notes
The prefix be- is inseparable and does not take stress; use 'beeinflussen' for both direct influence and indirect effects. In perfect tenses the auxiliary is 'haben'.