Simple:
* The sailor untied the boat from the dock.
* She untied the ribbon and opened the present.
More complex:
* The prisoner was able to untie his hands and escape.
* After the storm, the crew untied the sails to catch the wind.
* It took hours to untie the tangled fishing line.
* The dog untied its leash and ran away.
Figurative:
* He felt untied from his past, ready to start anew.
* Her words untied the knot of fear in her heart.
As a noun:
* The untie was quick and easy. (This is less common but grammatically correct)
These are just a few examples. The way "untie" is used will depend on the specific context of your sentence.