The introduction is the first paragraph in your essay, and it should accomplish a few specific goals.
1. Capture the reader's interest.
It's a good idea to start your essay with a really interesting statement, in order to pique the reader's interest.
Avoid starting out with a boring line like this:
"In this essay I will explain why Rosa Parks was an important figure."
Instead, try something with a bit of a surprise factor, like this statement:
"A Michigan museum recently paid $492,000 for an old, dilapidated bus from Montgomery, Alabama."
The second sentence sounds much more interesting, doesn't it? It would encourage most people to keep on reading.
(Your first sentence should be CLICK BAIT!!)