Rutul, these value are avaiable only when the worklfow is executing and not during preview of the workflow or planning. Also the command with "Get" should be after the command with "Add" in the workflow execution.I used the two lines you have mentioned in two different commands and can see that the value available in the second command.
No, Add and Get are usually to be used in different commands. The only condition is that the command with Add should be before the command with Get in the workflow. And you can see the values only when you execute the workflow.