'at least' is an adverbial phrase that is used to indicate a minimum number or amount, to emphasize a positive aspect in a negative situation, or to moderate a statement.
You should drink at least eight glasses of water a day.
The weather isn't great, but at least it's not raining.
I'm not a fan of his latest movie, but at least the soundtrack was good.
'at least' is often used for consolation or to find a silver lining in a situation.It can also be used to emphasize the importance or significance of something. 'There were at least a thousand people at the event.' A common mistake is using 'at least' where 'at last' (meaning 'finally') is intended 'He arrived at last' (meaning he finally arrived) vs. 'He brought at least three friends' (meaning he brought three or more friends).