RealHeavyDude and Tom are right in saying that it would help when you explain why you ask the question. Also telling us what version you are on is helpful. I was going to say something similar at the time but only had a few spare minutes so I decided to answer your questions instead. Don't forget that the people that use this forum and post answers to questions are generally all busy IT professionals that use their spare time to help you.
I could also have pointed to the online help and OE manuals as two of the three things you asked are pretty clearly stated in there. Did you do any investigation of your own? The question about the buffers you could definitely have investigated yourself by writing a few simple lines of code. Did you try any of that?
In any case, I hope your question was answered and that next time you will provide a bit of background and detail on your environment, versions and what you have done so far to try and resolve problems or questions. If you do that I am sure you will get a much better response