Oops, yeah you should probably swap offset[0] for x and offset[1] for y. There have been many times i've dealt with 2D arrays in rendering where Y represents index[0] for the row, and X represents index[1] for the values in the list, in any case its not really relevant here.
In the case of Pygame, 0 by 0 would be the upper left corner of the screen, so from there objects can be placed around the screen like so:
X by Y: Object does not move
-X by Y: Object moves left
-X by -Y: Object moves to the upper left
X by -Y: Object moves up
+X by -Y: Object moves upper right
+X by Y: Object moves right
+X by +Y: Object moves to the lower right
X by +Y: Object moves down
-X by +Y: Object moves lower left
So, lets say you have a screen resolution of 640 by 480. Now lets say you have a sprite thats 32 by 32, with an offset of 0 by 0, this would put the upper left of the sprite in the upper left of the screen. If its position was 320 by 320, it would be near the middle of the window, but not exactly, you'd need to adjust for the size of the sprite itself, so 320-(sprite.width/2) by 320-(sprite.height/2) would center it in the middle of the screen. In the case of the sprite being at -320 by -320, it would be completely off the screen and invisible as anything less than 0 aren't drawn to the screen, so -320+sprite.width = -288 by -320+sprite.height = -288, both are negative values, so the sprite isn't drawn.
In the case of the background, you could take a background image thats 1280 by 960 with an offset of 0 by -480, which would put the left side of the image to the left edge of the window, and the bottom of the image to the bottom of the screen. By moving the player character right you'd subtract the X offset, which would move the background image left giving the illusion of the player moving to the right, or by jumping you could add to the Y offset moving the image down, giving the illusion the player is jumping up.
As mentioned, I can provide a working example demonstrating this.
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BrushTone v1.3.3: Accessible Paint Tool
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AudiMesh3D v1.0.0: Accessible 3D Model Viewer