Hi Swati, Both MAT and CAT are entrance examinations that management colleges accept. There are several institutes which accept both. Both are fairly popular as well.
However CAT is the exam which helps you most and is accepted by the best B-Schools in India.
On the other hand MAT is the easier version. Since you have chosen to prepare please focus on CAT only, it covers the preparation for MAT.
Course wise there is no difference in the syllabus of two, only the level of questions are different. Questions in CAT are much difficult from those of MAT. CAT is conducted once every year and MAT is conducted four times in a year
of course preparing for CAT makes you even well prepared for MAT.
Best of luck.!