Parameters are place holders to keep the values that are subject to change. For example, if you have a different URL property for an API App hosted for development, test, and production, then it is viable to have a parameter defined that we can change at deployment time.

The basic structure for parameters is shown here:

"parameters": { 
 "<parameter-name>" : { 
    "type" : "<type-of-parameter-value>", 
    "defaultValue": <default-value-of-parameter>, 
    "allowedValues": [ <array-of-allowed-values> ], 
    "metadata" : { "key": { "name": "value"} } 
  } 
} 

Here is the code view where we have a parameter named useremail within the parameters section:

Once the parameters are defined, we can use them within Logic App workflow repetitively using workflow expression language.