A beginner's basic question

Hello everybody ,

I am new to Abap development and just starting out to play around in a test system at my disposal.My question is this .....

I read about Explicit and Implicit Enhancement Options being present in Standard programs. As far as possible ,I would like to use this methodology and thus avoid having to take up an object key(Access Key) for an object (say SAPMV45A).

But I donot find an explicit (or Implicit) enhancement point at the place I need to modify in the above object. What do I do ? DO I ....

a) Take up an Object Key and actually modify the source code at the point where I would like to .

b)Take up an Object key and introduce an Explicit Enhancement Option at the point I would like to ...and then code out my actual modification in the enhancement implementation for that option / Spot.

Is there any way ,I could go about this modification without taking up an object acess key....I have heard (perhaps wrongly) that User/Customer Exits are no longer the thing to do in the current version that we use (Netweaver 2004) . How about BADIs.(Business Application Add ins) .Would this need an object key for the above object (SAPMV45A) .

I appreciate any clarification that the forum can provide and would gladly help you with your points tally .

Thanks,

Nk