Hello Karen ,
Comparative is when you compare two persons,objects or anything . In this case the adjective,which describes this comparison will take a certain form :
ADJECTIVE + ER ( than ----- )
For example :
My car is nice . Karen's car is more nice
In this case you will say :
Karen's car is nicer than mine .
Or just : Karen's car is nicer .

Superlative :
When you state that a person or an object is holding "super" description in comparison with other persons or objects and it is formed as follows:
ADJECTIVE + est
For example :
In the last example , Karen's car is nicer than mine. Susan's car is even nicer than Karen's .
That would make it :
Susan's car is the nicest .
Another example :
My house is big , his house is bigger but Sue's house is the biggest of them all .

Present Perfect :
It is the tense that describes an action that started in the past and is extended to the present, it is not terminated or has JUST terminated .
It is formed as follows :
Verb to have + Participate of the verb
example : do I have done
eat He has eaten
He has just finished his work. ( Here the "work" started in the past and is JUST terminated at the moment or a little before the moment he said this sentence.
:)