what does this line mean

EACH RESTRICTION ENDONUCLEASE FUNCTION BY INSPECTING THE LENGTH OF A DNA SEQUENCE.

This line means that any restriction endonuclease functions by "scanning" or inspecting the length of a DNA molecule. Once it encounters its particular specific recognition sequence which is pallindromic , it will bind to that site and makes cut at the restriction site in both the strands of DNA molecule generating sticky overhanging ends.