If you transpose something, you change the order. You could transpose the phrases in that first sentence by writing, "You change the order if you transpose something."
In music, you also transpose when you change the key. When a song is a little high for you, you can transpose it to bring it down into your natural range. In math, to transpose is to move something from one side of an equation to another. In the equation x + 3 = 2y, you can solve for x by transposing the 3 to the other side of the equation, which will change its sign and give you x = 2y - 3.