Meaning of arrows in 3D representation of proteins
The flat arrows are a cartoon representation of β-strands (one type of regular hydrogen-bonded secondary structure). The direction of the arrow is the direction of the amino acid sequence (arrow head pointing towards the C-terminus). 

The thin wires are regions with no regular structure.

There are also two small green spiral ribbons in the foreground left and right, which represent α-helices (the other main regular secondary structure).