How did Lady Macbeth help Macbeth in murdering King Duncan?

I'm not sure from the phrasing of your question whether you mean "How did Lady Macbeth help Macbeth to murder Duncan?" or "How did Lady Macbeth help Macbeth achieve his goals in encouraging him to murder Duncan?" so I will answer both questions.
Lady Macbeth is an ambitious woman who wants her husband to succeed, both for his own purposes but also because it will make her more powerful. She believes that in order for Macbeth to be able to become king, as was prophesied, they must first take the opportunity to kill the current king, Duncan, when he is staying with them.
In terms of how Lady Macbeth actually helps Macbeth commit the murder, we can find examples of the practical assistance she provided in Act II Scene II. Duncan's bedroom was guarded, but Lady Macbeth disposed of the problem of the guards—she says she has "drugg'd their possets" so that they would fall asleep. She also says that she "laid their daggers ready / He could not miss 'em." As such, she has set the scene for Macbeth to be able to murder Duncan easily.
In broader terms, she also "helps" Macbeth to commit the murder by telling him that he would be "a coward in thine own esteem" if he does not commit it—"When you durst do it, then you were a man." Lady Macbeth insults Macbeth's masculinity as a means of persuading him to commit the murder, encouraging him to "screw [his] courage to the sticking-place."