What type of sentence is this? Why do we use the Past Participle?
I took this sentence from a game (Call of duty black ops 2).
Get the party started with a random rotation of Gun Game, Stick and Stones, One in the chamber, and Sharpshooter.
We can use the verb phrase to get {something}{verbed or verbing} to mean "to cause something or someone to enter the state expressed by the present-participle, or to achieve the state expressed by the past-participle".
To get the large car rolling, it took the three of us pushing.
To get the party started, she turned on some dance music.
To get the dinner cooking, he turned on the burner to preheat the skillet.
To get us thinking, the teacher posed a hypothetical.
To get the champagne chilled, the waiter put it in a bucket of ice.
To get the problem solved, she phoned the senator.
To get the term paper written, he pulled an all-nighter.
To get the news circulated, they posted it on Twitter.
With the past-participle form, only verbs which take a noun-phrase direct object may be used.
With the present-participle, the verb may be intransitive.