Cordially,
Go to www.arn.org and read anything by Philip Johnson, William Dembski, Michael Behe or Jonathan Wells.
The basic idea lies in what Philip Johnson describes as "specified complexity" or simply information. It is the difference between this sequence of 17 letters, LRINTSPVBMWNRJNQP, this sequence of 17 letters, ABABABABABABABABA, and this sequence of 17 letters, MARYHADALITTLELAMB. The first is unspecified and not complex. The second is specified but not complex. The third is specified and complex.
ID theorists observe natural phenomena that carries information, and try to determine how best to explain the existence of the information. The information can be categorized as information arising from accident, natural forces, chance or design.
Simply stated, it is more reasonable to believe that the letters SOS written in the sand were designed rather than a chance occurrence. Similarly, it is more reasonable to believe in a designer of "irreducibly complex" parts of an organism, such as the human eye, rather than creation by blind chance.