At first is used to talk about the beginning of a situation.
At first is often followed by but.
In any other cases, we usually use first.
Examples
I first met her at a work.
TheOpenDictionary
Search for word, phrasal verb or idiom
Phrasal Verb Of The Day
Description
To remove someone from a position on something such as a committee by voting
Get a FREE WORD, PHRASAL & IDIOM
of the day in your inbox
Meaning
Start something over