Android beginner difference between padding and margin [duplicate]

Question

Margin

Margins make up the vertical and horizontal areas between elements. If elements have no margins around them, they will bump right up against each other. In other words, he space outside of, or between, elements is what comprises the margin areas.

Padding

The padding of an element is the horizontal and vertical space that’s set around the content area of the targeted element. So padding is on the inside of a box, not the outside.

Padding is for inside/within components. Eg. TextView , Button, EditText etc.
Eg. space between the Text and Border

Margin is to be applied for the on-outside of the components.
Eg. space between left edge of the screen and border of your component

Visual representation is great in : Difference between a View's Padding and Margin

With Padding, i have seen a difference in 2.2, 2.3 and say 4.3, 4.4
in such cases:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:text="ASDFGHJKL" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingLeft="15dp"
        android:text="@string/hello_world" />

</RelativeLayout>  

Also, check the use of dimens:
http://developer.android.com/guide/topics/resources/more-resources.html

In Simple words .. if you want to take your widget like TextView, EditText far away from other. You should use margin from top,right,left,bottom.

By increasing padding it will increase the inner spacing not making the widget far apart from others..

Like buttons, for example, the characteristic button background image includes the padding, but not the margin. In other words, adding more padding makes the button look visually bigger, while adding more margin just makes the gap between the button and the next control wider.

Margin: Between border and its parent layout

Padding: Between content and border

refer to this

The difference between margin and padding and use cases are clearly explained by +Nick Butcher in Udacity's video. Here's the excerpt:

...if you want the touchable area or the background of the object to be enlarged, then use padding, otherwise use margin...

what is the difference fundamentally between padding and margins ?

For the differences - Rohan Khandwal has shared a very perfect link.

Would the behaviour differ depending on O.S. and devices?

Now If we are talking about the behaviour of the view which has been given diffrent margins & padding. Then It will definitely look diffrent in different devices with diffrent resolutions. Thats why we are given diffrent dimen/values/layout folders which have their own meanings.