XBee not sending right away

The XBee's are of the chip-kind, I really don't know what kind they are, besides that..
Although, I think the code is actually what's messing with me.
I changed a few things in the receiver code, and that seemed to have changed a few things.

Do you have an example of a really simple receiver code? My current one is:

String str = "";
  
  if(Serial.available() > 1)
  {
    while(Serial.available())
    {
      char c = Serial.read();
      str.concat(c);
    }
  } 
 
  if(str != "" && str != "\n")
  {
    Serial.print("New: ");
    Serial.println(str);
  }

But that still seems to kind of buggy, my output right now from the console is:

New: F1
New:

But it gets even buggier if I send more data..