@Minisha_M, Data which are required for process execution can be stored in camunda data store. Other than that you can store in the other datasource of business application.
Form fields captured in user task forms are stored in camunda database, you can’t mark it as transient and related ticket can be found here, Transient Variable Availability.
For each active task instances, the variables are stored in ACT_RU_VARIABLE table, and the variables of completed task instances are stored in ACT_HI_VARINST table.