Okb9 and 3keh differecne

I'm trying to understand the difference between OKB9 and FAGL3KEH. And at the time of asset acquire entry will be asset dr to vendor credit.. in that case how will document splitting take place because both items are balance sheet items how will business area wise or profit center wise splitting will take place...in case of balance sheet account how will document splitting take place.

For that will we use FAGL3KEH OR OKB9. Please explain.