Jesse Huang said:
(1) He said he will come. (right?)
(2) He said he would come.
What's the difference between them? :?
They can both mean the very same thing. This brings us to "reported speech". In most cases, when one reports what another has said, one backshifts the entire sentence to past tense. An exception would be "early" reported speech, when the report comes soon after the original statement.
Let's say that Mary invites John to a party and John says "Yes, I will come." If Mary turns to Sally and reports, she may say "John says/said that he will come. Several hours later, "John says he will come" no longer works very well. At that point, Mary would say "John said that he will/would come." After more time elapses, perhaps the following day, it would be more likely to say "John said that he would come." "Would" here is being used as the past tense of "will", not as a sign of a conditional. There are many variations of this area of English.