Normal flow is the way thats elemnts are displayed. Block and Inline elements are rendered in the order they've been written. Margin-left of block elements are aligned vertically with the margin-left of their container element. Margin-left of inline elements are aligned "in-line" (horizontally) with sibling elements..
Relative position allows you to move an element (top, right, bottom, left) relatively to its initial position. Elements which have relative position are still in the normal flow : notice the second inline elements which is still in the same position as before (normal flow).
ex: left:200px; top:-30px;
Floating elements are take out the normal flow. The margins are ligned up with the margin left or right of the container element (float:left; or float:right;).The following elements are placed in the empty space of the normal flow.
ex: float:right;
Absolute position allows you to place your element (top, right, bottom, left) according to the first positioned parent element.
ex: top:0;right:0;
Fixed position allows you to plce your element (top, right, bototm, left) according to the window wiewport.
ex: bottom:0;left:0;