pusten
to blow
To push air deliberately out of the mouth in order to cool something down, blow something out, or move something away.
Puste bitte die Kerzen auf dem Kuchen aus!
Please blow out the candles on the cake!

to blow / pant
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to blow
To push air deliberately out of the mouth in order to cool something down, blow something out, or move something away.
Puste bitte die Kerzen auf dem Kuchen aus!
Please blow out the candles on the cake!

The verb 'pusten' (to blow) is often combined with prepositions that indicate a direction. Common constructions are 'auf' (+ accusative), 'in' (+ accusative), or 'von' (+ dative).
Puste bitte nicht auf die heiße Suppe, das macht man nicht.
Please don't blow on the hot soup; that's not something people do.
Two very typical situations for 'pusten' (to blow) are blowing out candles on a birthday cake and comforting a child by blowing on a small wound or scratch.
Das Geburtstagskind pustete alle Kerzen auf einmal aus.
The birthday child blew out all the candles at once.
In the colloquial meaning 'schwer atmen' (to breathe heavily), you can usually recognize the context from a preceding description of physical exertion. Typical situations are climbing stairs, running, or doing sports.
Nach dem Sprint zum Bus musste ich erst mal ordentlich pusten.
After the sprint to the bus, I first had to really pant.
The meaning 'einen Alkoholtest machen' (to take a breathalyzer test) is used exclusively in the context of a police traffic stop. Signal words are 'Polizei' (police), 'Kontrolle' (check/traffic stop), or 'angehalten werden' (to be pulled over).
Der Fahrer musste anhalten und für den Alkoholtest pusten.
The driver had to stop and blow for the breathalyzer test.
to blow
'blasen' and 'pusten' can mean the same thing in many everyday situations: you push air out of your mouth, for example onto a candle or onto hot food. 'pusten' usually sounds more everyday and fits especially well when you deliberately blow air from your mouth onto something. 'blasen' is more general and can also be used for devices or strong wind. The words are therefore easy to confuse. In simple situations involving the mouth, both are often possible, but 'pusten' often sounds more natural and personal.

Bitte puste kurz auf den Tee, er ist noch sehr heiß.
Please blow on the tea for a moment; it is still very hot.
Erik bläst die Kerzen auf dem Kuchen aus.
Erik blows out the candles on the cake.