gefrieren
to freeze
To change from a liquid to a solid state due to cold; to turn into ice.
Bei null Grad Celsius beginnt Wasser zu gefrieren.
At zero degrees Celsius, water begins to freeze.

to freeze
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to freeze
To change from a liquid to a solid state due to cold; to turn into ice.
Bei null Grad Celsius beginnt Wasser zu gefrieren.
At zero degrees Celsius, water begins to freeze.

Since 'gefrieren' (to freeze) describes a change of state from liquid to solid, the perfect tense is always formed with the auxiliary verb 'sein' (to be).
Der See ist über Nacht komplett gefroren.
The lake froze completely overnight.
The prefix 'ge-' is inseparable. It remains firmly attached to the verb in all conjugations and sentence positions.
Ich hoffe nicht, dass die Heizung ausfällt und die Rohre gefrieren.
I hope the heating doesn't fail and the pipes freeze.
When a person is extremely cold, this is often expressed with a dative construction. The person is in the dative, while the freezing body part is the subject.
Zieh deine Handschuhe an, sonst gefrieren dir die Finger.
Put your gloves on, or your fingers will freeze.
In the figurative meaning of becoming rigid, 'gefrieren' (to freeze) often refers to facial expressions or feelings. Typical subjects are 'das Lächeln' (the smile), 'die Miene' (the expression), or 'das Blut in den Adern' (the blood in one's veins).
Als er die Gestalt im Dunkeln sah, gefror ihm das Blut in den Adern.
When he saw the figure in the dark, the blood froze in his veins.
to melt
'schmelzen' and 'gefrieren' describe opposite changes caused by temperature. With 'schmelzen', something solid becomes liquid through heat, for example ice or chocolate. With 'gefrieren', something liquid becomes solid through cold, usually turning into ice. So the difference is the direction: warmth makes things liquid, cold makes things solid. These words are especially useful when talking about water, ice, snow, or food.

Über Nacht gefriert das Wasser in der Regentonne.
Overnight, the water in the rain barrel freezes.
In der Sonne schmilzt das Eis im Glas sehr schnell.
In the sun, the ice in the glass melts very quickly.