I will explain:
1st step - rtrim('!!athen!!','!') it's output come like this "!!athen"
2nd step - ltrim('!!athen','!') its output come "athen"
3rd step - trancelate('athen','an','**') its output come like this "the"
4th step - replace('the','*','trouble')
finally, its output being look like this "trouble the trouble"