Partner just opened with a 2  bid which is strong and artificial. (He does not necessarily have length in Clubs and could even be void in the suit.) But he does have a monster hand: 21+ points or a hand with 4 or less losers (9 or more winners). 

A. 2  Response with a Weak Hand. When partner opens 2  and you have a poor hand of 5 or less points you respond 2 . Bid your 5+ card suit with 6 or more points. With 6 or more points and no 5 card suit, respond 2 No Trump; with 10 or more points, 3 No Trump.
PROS: you show you suit and/or point count on your first bid. 
CONS: if you bid No Trump and No Trump is the final contract, the 2  opener is the Dummy with the strong hand exposed. 

B. Step Response. Again partnership agreements will determine where the steps occur. An example might be;
 

0 - 3  points == respond 2  4 - 6 points  == respond 2  6 - 9 points  == respond 2  10 + points  == respond 2 or 3 No Trump

PROS: the 2  opener can easily place the hand in slam, game or a part score. 
CONS: there are quite a few.  The first is that the responder uses up bidding room especially with the 2 No Trump or 2  bid. Another minus is having to remember the steps and also to remember to not to forget that you are playing steps. And the third con is that responder can inadvertently bid a suit that becomes the suit for the final contract. This makes 2  opener the dummy with the strong hand exposed.

C. 2 Diamonds Waiting. This is becoming (or has become) 
one the most popular response to a 2 opener.  The 2  bid over a 2  opener is purely artificial. You do not necessarily have length in Diamonds. If you do have a Diamond suit, bid it again on the next time around. If you elect to respond 2  , 2 , 3  or 3 , then you are have a good 6 card suit (3 of the 4 top honors) with possible slam Interest.
PROS: the 2  response keeps the bidding low and gives the strong hand the ability to describe his hand first and even be the first No Trump bidder. 
CONS: There are really no cons with this bid other then having to remember that you are playing 2  waiting.

D. The Second Negative. This convention enables the responder to show partner a super weak hand (something like a jumbo shrimp) with 3 or less points. After the 2  opener rebids a suit, responder bids the next higher suit (3  over 2 ). This says "Partner, I have great weakness and will pass  your next bid." See example 1  below. 
   

1.   PARTNER             YOU              2   ====>   2               2   ====>   2

Of course if you did have a spade suit with a decent hand you would bid again. Either Spades, No Trump or another suit.

TIPS: 
1. After your 2  response try to bid only 5+ card suits. 
The 2  opener should also rebid only 5+ card suits.
 2. A jump to game (by 2  opener or responder) is a 
shut out bid. It says "Partner pass, this is all I think we can make."  This means that a rebid of a suit below game level shows a good hand , maybe with slam possibilities. 
   

2.   PARTNER          YOU             2   ====> 2              2   ====> 4

In example 2 you are saying "Partner, I have a very weak hand with some Heart support. I do not think we should go higher. " 
   

3.  PARTNER      YOU          2  ====> 2           2  ====> 3           4  ====>  ?

  "Partner, I have Spade support and we might have slam." Cue bids will now show first round  control. In Example 3 partner has a void in Hearts or the A . You or your partner might want now to use the Blackwood convention or just jump to slam.