Previous, Former, Last

These words look alike, right? Well, sometimes they are used in similar ways.

It depends on the context and the purpose of what you want to say.

The last president was not good at public speaking.
The previous president was also not good at it.
However, the former president was a bit better.

There is an order here.
"Last" deals with immediate/recent past.
"Previous" deals with before "last".
"Former" occurred any time in the past.

Former president, Ronald Reagan
Previous president, George Bush Sr. （1989-1993）
Last president, William Clinton (1993-2001)

Reagan -> Bush, Sr. -> Clinton -> Bush (Current President)

With adverbs, the words are different.
Previously is used to talk about something before another thing.
Lastly is used to talk about the last thing.

Previously, I told you about ... （前回、～について話しました）
Lastly, I want to tell you about...　　（最後に、～について話したいと思います）

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context : 文脈
adverb : 副詞