We discussed the details of observations and methodology adopted to analyse the Ca-K spectrohelio-grams obtained at Kodaikanal observatory (KKL) during the period of 1905 - 2005. We have given the derived values of threshold of the intensity contrast to detect the various Ca-K line features such as plages and networks. Using this procedure we have studied the variation of Ca-K plage areas, enhanced network (EN) and active network (AN). We have derived the areas of all the three features for all the data available at Kodaikanal observatory to study the long term variations on the sun. Further, we have investigated the variation of intensity contrast of these features with time with the temporal resolution of 3 months assuming the quiet chromosphere remains unchanged during the period of 1906 - 2005 and found that average intensity of plages, EN and AN varies with solar cycle phase being less during the minimum phase. In addition, the average intensity of plages varies with a long period being maximum during the solar cycle number 19 (strongest solar cycle during the 20th century). The correlation between intensity of the Ca-K emission and strength of the magnetic field suggests that the magnitude of the magnetic field is also related with sunspot number and plage area of a solar cycle. It may be noted that the variation of intensity of networks with time has been studied for the first time.