At last is used to say that something happens after waiting or trying for a long time, and when you’re happy about it. Lastly is used to refer to the last action in a series, the last item in a list or to introduce the last point you want to make.
at last It’s nice to be back home at last. At last, we arrived! At last you understand what I’m trying to say! lastly Open the bin, load the paper and lastly turn on the printer. You have to add salt, and lastly oil Lastly, I would like to remind you that our next meeting is on August 10th