how can identify the users that were added recently on appian

You can get the timestamp of when the users were created and some other actions in "user_management.csv" inside "audit/_" in System Logs. Read this file using Log Reader plugin and filter with columnName: "Action" and value equal to "Create".

user() function can also give you the createdOn date of a particular user: 

user("username","created")

a!localVariables(
  local!allUsers: getallusers(startIndex: 1, batchSize: - 1),
  a!flatten(
    a!forEach(
      local!allUsers,
      if(
        or(user(fv!item, "created") > now() - 30),
        fv!item,
        {}
      )
    )
  )
)

a!localVariables(
  local!allUsers: getallusers(startIndex: 1, batchSize: - 1),
  a!flatten(
    a!forEach(
      local!allUsers,
      if(
        or(user(fv!item, "created") > now() - 30),
        fv!item,
        {}
      )
    )
  )
)