33  And with great power gave the apostles witness of the resurrection of the Lord Jesus: and great grace was upon them all.
34  Neither was there any among them that lacked: for as many as were possessors of lands or houses sold them, and brought the prices of the things that were sold,
35  And laid them down at the apostles' feet: and distribution was made unto every man according as he had need.

This was a freewill offering.  No one was obligated.  They did it because they wanted to.  If you want to give, you can.  If you genuinely believe God is moving on your heart to give to someone or some cause, then make sure it's God moving on your heart and then obey Him, and don't be concerned with the results.  He may bless financially or He may bless a different way.

36  And Joses, who by the apostles was surnamed Barnabas, (which is, being interpreted, The son of consolation,) a Levite, and of the country of Cyprus,
37  Having land, sold it, and brought the money, and laid it at the apostles' feet.
5:1  But a certain man named Ananias, with Sapphira his wife, sold a possession,
2  And kept back part of the price, his wife also being privy to it, and brought a certain part, and laid it, at the apostles' feet.
3  But Peter said, Ananias, why hath Satan filled thine heart to lie to the Holy Ghost, and to keep back part of the price of the land?

As a side note, Peter said they lied to the Holy Spirit and then Peter clarified and said they lied to God.  Thus proving the Holy Spirit is God.

4  Whiles it remained, was it not thine own? and after it was sold, was it not in thine own power? why hast thou conceived this thing in thine heart? thou hast not lied unto men, but unto God.

Peter said it was theirs to do with as they pleased.  Even after they sold it, it was still their own to keep or do whatever they chose.  Their sin was not keeping back part of the money - they could have kept some of it, all of it, or not sold the land at all.  They wanted the PRAISE so they sold the land and pretended to give it all - and lied in the process.  There was their sin.

5  And Ananias hearing these words fell down, and gave up the ghost: and great fear came on all them that heard these things.
6  And the young men arose, wound him up, and carried him out, and buried him.
7  And it was about the space of three hours after, when his wife, not knowing what was done, came in.
8  And Peter answered unto her, Tell me whether ye sold the land for so much? And she said, Yea, for so much.
9  Then Peter said unto her, How is it that ye have agreed together to tempt the Spirit of the Lord? behold, the feet of them which have buried thy husband are at the door, and shall carry thee out.
10  Then fell she down straightway at his feet, and yielded up the ghost: and the young men came in, and found her dead, and, carrying her forth, buried her by her husband.

What lesson do we learn?  If you're going to give to a cause, make sure it's God's will for you and obey God.  Don't put on a show for others.  Don't be pressured by men - let God speak to your heart.

These disciples gave their possessions to the church and the apostles distributed to all as they needed.  But what happened a few years later?  They had run out of money!  Why?  Because God didn't tell them to live like a commune - that was their own choice.  How do I know they ran out of money?  Turn to Romans 15:

25  But now I go unto Jerusalem to minister unto the saints.
26  For it hath pleased them of Macedonia and Achaia to make a certain contribution for the poor saints which are at Jerusalem.
27  It hath pleased them verily; and their debtors they are. For if the Gentiles have been made partakers of their spiritual things, their duty is also to minister unto them in carnal things.

The Corinthian church (Gentiles mostly) had taken up a collection for the "poor saints" at Jerusalem.  The poor saints became poor because they gave everything away even though the Holy Spirit did not tell them to.  What Christ told one man (the rich young ruler) was to point out to that man that he had a covetous heart - it was not to be the standard for the whole church for all of time.

These saints became poor because they did not follow the leadership of the Holy Spirit fully, and now Paul is taking up contributions on his church planting travels to relieve the Jewish believers at the church of Jerusalem.

From 1 Corinthians:

16:1  Now concerning the collection for the saints, as I have given order to the churches of Galatia, even so do ye.
2  Upon the first day of the week let every one of you lay by him in store, as God hath prospered him, that there be no gatherings when I come.
3  And when I come, whomsoever ye shall approve by your letters, them will I send to bring your liberality unto Jerusalem.

Thus we see how God used the believing Gentiles to relieve the suffering of the Jewish believers, and we thank God for that.

Give as God commands you, but make sure it's God moving your heart and not some shyster preying on you trying to make you feel guilty before God.  God loves a cheerful giver.