Points, lines, planes, and other geometric figures exist only in an abstract way within your mind.  Just like everything else.

Carl Sagan Explaining 5th Dimensional Beings (Except, not really...)

Carl Sagan.  Duration_9_29

Specifying Planes

Khan Academy.  Duration_4_11

Basic Geometry_Language and Labels

Khan Academy.  Duration_12_57

Measuring Segments_Ruler Postulate

Khan Academy.  Duration_1_28

Segment Addition Postulate

Khan Academy.  Duration_3_39

Hidden Dimensions: Exploring Hyperspace 

Brian Greene.  Duration_1_27_15

Imagining the Tenth Dimension

Having trouble imagining more than 3 dimensions?  What about the 10 or 11 promised by string theory?  You wouldn't be alone.  To help us, some Canadian guy (Rob Bryanton) put together this animation.  Duration_12_45

Geometry 2(B) derive and use the distance, slope, and midpoint formulas to verify geometric relationships, including congruence of segments and parallelism or perpendicularity of pairs of lines 

Geometry 4(A) distinguish between undefined terms, definitions, postulates, conjectures, and theorems