re-sizing the background and others

How do I resize my pixels? What is the background length for flash games and also how can I change the same background to make it for the IOs or Android version?
How do I resize it and how to I change it's lengths?

I'm not sure what you mean.  I'm making a PC game that is running using Flash and I made my backgrounds two screen heights by two screen widths (it's a platformer with a big of height to it).  Then I set them to loop and put a slight paralax effect on them.  I imported large images with the 4x import setting and they look great on a full screen. 

What I mean to say is every graphic that I make is too big for my game. Like the character or objects. What should I do to make it into a perfect size for my game?

How big are your screens?  If I were you I would turn on the "see screen bounds" in your build screen and turn on the grid and then take a look. Each box  within the player area is 32 pixels if you are using regular sized art. Chances are that most of what you are going to use in your game will be a box, or two, or three. That means most of your art won't be bigger than 96 x 96 (3 boxes x 3 boxes). Once you import it you can change the collision shapes to make it exact. If you want art that will look good on a big screen, do everything 4x as big and set your import settings to 4x.