What was the original meaning of the word 'computer' in the early 17th century?

A person who performed calculations.

What was the significance of Charles Babbage's Analytical Engine?

It was a general-purpose computer that could be programmed.

Ada Lovelace, for writing hypothetical programs for the Analytical Engine.

I can describe the major milestones in the history of computing.

1
The earliest computing device was the abacus, which was invented in Mesopotamia around 2500 BCE.
2
Before devices were called computers, the word 'computer' referred to a job title for a person who performed calculations.
3
Charles Babbage designed the Difference Engine and the Analytical Engine, earning him the title of the 'father of computing'.