To install the serverless framework open-source CLI, execute the following command on yout terminal:
npm install -g serverless
Once you've installed it, you should be able to execute the following command
$ serverless -v
x.x.x
Have a look at this thread to know more about how to deploy a serverless service: https://www.edureka.co/community/57664/create-and-deploy-a-serverless-service-on-linux