What does Buddhism say about the consequences of good and bad behaviour?

Disclaimer: My answers may lean towards the Theravada tradition.

Does Buddhism believe in rebirth?

Yes. But there is no permanent soul that transmigrates from one body to another. Instead, just as how the flame of one candle could light another, one is reborn with the final state of mind (representing the overall volitional tendencies cultivated during life) of the previous birth shaping the circumstances of the future birth. You can read the essay The Truth of Rebirth And Why it Matters for Buddhist Practice by Thanissaro Bhikku. There is a section of another essay by Nyanatiloka Mahathera that discusses Kamma and Rebirth.

There is an general belief in almost all religions that our good and bad will be carry forwarded to next and next to next generation and all, what does Buddhism say about that?

The past volitional actions of thoughts, words and deeds shape the future circumstances according to the Ekamsena Sutta (quoted below). There is a good essay on Karma: A Study Guide, again by Thanissaro Bhikku.

"Given that I have declared, Ananda, that bodily misconduct, verbal misconduct, & mental misconduct should not be done, these are the drawbacks one can expect when doing what should not be done: One can fault oneself; observant people, on close examination, criticize one; one's bad reputation gets spread about; one dies confused; and — on the break-up of the body, after death — one reappears in the plane of deprivation, the bad destination, the lower realms, in hell.

"Given that I have declared, Ananda, that good bodily conduct, good verbal conduct, & good mental conduct should be done, these are the rewards one can expect when doing what should be done: One doesn't fault oneself; observant people, on close examination, praise one; one's good reputation gets spread about; one dies unconfused; and — on the break-up of the body, after death — one reappears in the good destinations, in the heavenly world.

However, according to the Sivaka Sutta, not everything we experience is the result of past kamma.

"There are cases where some feelings arise based on phlegm... based on internal winds... based on a combination of bodily humors... from the change of the seasons... from uneven care of the body... from harsh treatment... from the result of kamma. You yourself should know how some feelings arise from the result of kamma. Even the world is agreed on how some feelings arise from the result of kamma. So any brahmans & contemplatives who are of the doctrine & view that whatever an individual feels — pleasure, pain, neither pleasure-nor-pain — is entirely caused by what was done before — slip past what they themselves know, slip past what is agreed on by the world. Therefore I say that those brahmans & contemplatives are wrong."

Almost all religions says give a part of money to god and that will be honoured after death. What is Buddhism's stand on that?

Buddhism encourages Dana, the practice of giving. You can read the essay, Dana: The Practice of Giving for details. Here, giving is not to the gods, but to monks, guests, travellers, the sick and the needy. The manner and attitude of giving is very important. The essay will tell you much more. There is a whole sutta for this, the Dana Sutta. I quote from it here:

"Then there is the case of a person who gives a gift not seeking his own profit, not with a mind attached [to the reward], not seeking to store up for himself, nor [with the thought], 'I'll enjoy this after death.' Instead, he gives a gift with the thought, 'Giving is good.' He gives his gift — food, drink, clothing, a vehicle; a garland, perfume, & ointment; bedding, shelter, & a lamp — to a brahman or a contemplative. ... "Having given this gift with the thought, 'Giving is good,' on the break-up of the body, after death, he reappears in the company of the Devas of the Thirty-three. Then, having exhausted that action, that power, that status, that sovereignty, he is a returner, coming back to this world.

In many religions, if the leaders (monk, sadhu or whatever may be.. ) do something wrong other monks says that they will be punished after death by god,but they keep on doing it. If god punished him instantly many will be saved. But this is not happening. How does Buddhism look at this?

Surely one who does wrong would face the consequences of his words and actions. This applies to monks and religious leaders too.

Your question hints that a religious leader who preaches wrong views or encourages wrong actions would influence many towards the wrong path. Hence, if such leaders get punished instantly, many would be saved from going down the wrong path.

According to the Kalama Sutta, the onus is on the follower of the path to select his teachers wisely and to discern the right teachings wisely. There are some details on how to do this, in the sutta. Thanissaro Bhikku, the translator, has these comments for this sutta:

Although this discourse is often cited as the Buddha's carte blanche for following one's own sense of right and wrong, it actually says something much more rigorous than that. Traditions are not to be followed simply because they are traditions. Reports (such as historical accounts or news) are not to be followed simply because the source seems reliable. One's own preferences are not to be followed simply because they seem logical or resonate with one's feelings. Instead, any view or belief must be tested by the results it yields when put into practice; and — to guard against the possibility of any bias or limitations in one's understanding of those results — they must further be checked against the experience of people who are wise. The ability to question and test one's beliefs in an appropriate way is called appropriate attention. The ability to recognize and choose wise people as mentors is called having admirable friends.