I want to use my Stored Procedure's return a string value.
For send email which body is then string.
Have you found and tried the Stored procedure SQL action?
It should allow you to run a procedure, and then in a subsequent action it allows you to use the output as part of the action (e.g. sending the SQL procedure's output as part of the body of that email).
(Attaching a screenshot of where you can select this SQL action).
Feel free to post again in case you would like more details/help.
I use the Action "SQL Server - Execute stored procedure" in my flows.
and the value "ReturnCode" use in the Condition.
and, I want to use a string from the Stored Procedure's select.
In order to do this, you can use "select into" if that's what you really want to do.