Dear Afsar, to start a career in Cloud computing, you need to have basic foundation regarding topics like Networking, Computer Security, Computer Architecture and learn PL/SQL and Linux fundamentals. AWS and Azure are the two top Cloud  Service Providers in the market right now. So you can pick up any of them and do a certification course and have ample practical exposure. To become a successful Cloud Computing professional, you need to have thorough knowledge on Compute Services, Storage Services, Database Services, Networks or VPN, Load Balancing and Scaling, Cloud Monitoring and Application Migration.