Positioning Textures on screen

I am newer to this Unity world. I read few materials from Unity developers site for learning Unity basics.

But still i am not clear to positioning textures on screen both 2d and 3d. also i am not clear in camera concepts.

Is there want to set any particular value settings to camera for correctly display our GameObjects on Game View.

ie) my problem is if i positioning my GameObject on Scene view means it doesn't display on GameView. Even manually i change transition and rottationvalues also. After more lot of struggle i see that object on Scene view. I set projection as Orthograpic for 2d and Perspective for 3d. Shall i want to set any particular value settings to camera and objects.

Please give some guidelines to strong on unity basics.

Thanks in Advance.