frieren
to be cold
To feel a strong sensation of cold in one's own body.
Ich friere, kannst du bitte das Fenster schließen?
I'm cold; could you please close the window?

to be cold / freeze
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to be cold
To feel a strong sensation of cold in one's own body.
Ich friere, kannst du bitte das Fenster schließen?
I'm cold; could you please close the window?

The auxiliary verb depends on the meaning. When a person feels cold, the perfect tense is formed with 'haben' (to have). When something turns into ice, 'sein' (to be) is used.
Obwohl ich eine dicke Jacke trug, habe ich schrecklich gefroren.
Although I was wearing a thick jacket, I was terribly cold.
You can recognize the meaning of 'frieren' (to be cold / freeze) from the subject of the sentence. If the subject is a person, they are feeling cold. If the subject is a liquid or something containing water, it is turning into ice.
Das Kind friert, weil es ohne Mütze draußen spielt.
The child is cold because it is playing outside without a hat.
The past participle 'gefroren' (frozen) is very often used as an adjective. It describes the solid state of water or also frozen foods.
Vorsicht, die Stufen sind gefroren!
Careful, the steps are frozen!
If you want to say that a specific body part is cold, you can use the person as the subject or use the construction 'an' + dative.
Meine Hände frieren schon wieder.
My hands are cold again.
To express that the outside temperature is below 0°C, the impersonal construction 'es friert' (it is freezing) is used. The 'es' is a fixed, formal subject here.
Nachts hat es gefroren, deshalb sind die Straßen glatt.
It froze during the night, so the roads are slippery.
to tremble
'zittern' and 'frieren' can both occur in a situation involving cold. 'Frieren' describes the feeling: a person feels cold. 'Zittern' describes the visible movement of the body when the hands, legs, or whole body shake quickly. So you can be cold without trembling strongly, and you can also tremble from fear or excitement. Learners confuse the words because cold often causes both. Practical tip: use 'frieren' for the feeling of cold, and 'zittern' for the body movement.

Kannst du das Fenster schließen, weil ich friere?
Can you close the window because I'm cold?
Nach zehn Minuten im kalten Wind zitterten meine Hände.
After ten minutes in the cold wind, my hands were trembling.