"Too" is a multi-purpose intensifier in English. It can be used to add emphasis to an adjective or adverb: "too fast", "too slow", "too hot", "too cold", etc. In this way it is used similarly to very ("very fast", "very hot) but with a different nuance. "Too" implies something is "more than" -- more than expected, more than is possible, more than is tolerable, etc.
We spend too much money.
It's too sweet for me.
They move too quickly for the human eye to follow.
Superman is too strong to defeat with mere bullets.
In your example, "too" is used to emphasize inclusion. As you say, it works like "also".
She wants to go too.
The boy said he too would like some ice cream.
They normally raise just cattle, but this year they're raising sheep, too.
The comma before "too" is optional.