I am so confused about the verb " condescend" . It seems to be me that it has two meanings which is in opposite with each other.

eg ) He is too powerful and rich, you should

1) stoop to him for help.

2) condescend to him for help.

3) descend to him for help.

which one is mostly used in daily conversation.

eg. He is poor and no education but He

1) behave in a condescending way.

2) behave in a patronizing way.

which one is commonly used? what does it mean in this context?
There's only one core meaning of "condescend", which is to do something that you think is beneath you. Within this meaning, I guess you can do it graciously or ungraciously, though the "ungraciously" sense is, to varying degrees, often implied.

None of your first set of sentences (1-3) seem right to me. You do not normally "stoop", "descend" or "condescend" if you're approaching someone who's powerful and rich. (It's possible you could "stoop" in the physical sense of bowing, however.)

Your second set of sentences (1-2) are OK, and have similar meanings.

Edit: Sorry, not quite OK, it should be "He behaves..."
When used as a verb, condescend means to lower yourself, generally to be humble, though it is often used sarcastically (thereby, reversing the meaning).

Eg. "Would you condescend to move your car?", basically means, 'you arrogant sod, move your car now',

The more common use of condescend is as an adjective, such as in 'He behaved in a condescending way towards me'.

Perhaps, the Oxford English Dictionary can help you understand;

condescend v show that one feels superior; do something despite regarding it as beneath your dignity.