What is the possible start of career for a telecom Engineer and how to develop in it ?

Telecom in general terms is vast. we have many section like Transmission ,IP and Data ,Bss, Radio access or core Network... i hope you have learned basics in school. But when you come to the industry, its different story. cisco certification is useful for most of the sections. But vendor specific trainings are what help you perform good on daily routines. When you join the sector you'll join one of many departments and Trainings and materials you read should be tunes to that sector and to be effective you should read vendor specific documents. If you join Transmission you should know about PCM, SDH, WDM, Microwave and OTN technologies, like wise if IP and data deep knowledge of cisco is must. Radio access requires knowledge of GSM, UMTS ,LTE and ... Technologies.