as a noun, 'use' refers to the act of employing something or the state of being employed for a purpose. It can also denote the ability or capacity to be used.
'use' as a noun can be paired with prepositions like 'of' or 'for' to indicate the purpose or object of the use.
The use of smartphones has increased dramatically over the past decade.
What's the use of this device?
This room is of no use to us anymore.
'Use' can also refer to the benefit or advantage of something
'It's no use crying over spilled milk.' 'Of use' and 'to use' can be used interchangeably in some contexts, but they can have different nuances
'Is this of any use to you?' vs. 'Do you have a charger to use?'
as a verb, 'use' primarily means to employ for a specific purpose or to put into service. It can also refer to consuming or depleting something.
'use' can be used in various tenses and voices. It can be followed by a direct object to indicate what is being used.
I use a pen to write my notes.
She used all the flour for the cake.
Can you use this tool to fix the door?
'Used to' is a phrase that indicates a past habit or state 'I used to play basketball.' Avoid confusing 'use to' and 'used to.' The former is often incorrect unless it's in a negative statement or question in the past tense 'I didn't use to like coffee.'