First I'd like to tell you that you cannot say "explain me". Instead you should say "explain it to me" or "explain why 'was' is used", etc.
Now let me ask you a question about your example ("I was wondering if anyone could explain me.........."):
What does could explain mean? Is it:
1) past tense of "can explain" OR
2) a polite form of "can explain"
Which meaning does "could explain" have in your example? What do you think? Is it the past tense or just polite?
If you decided that it's polite (2), then you're correct!
And now we'll finally come to your question:
"I was wondering..." means basically the same thing as "I would like to know..." (polite form)
Hope that helps.