First of all, here's the best website I've found to help students read Shakespeare's plays:
Click on the title of the play you want (in this case Hamlet), then click on the act and scene. You'll find original Shakespearean language on the left and a modern-day "translation" on the right.
Here are several other really good websites about Shakespeare and his works and his times. Be sure to add ALL THESE to your favorites so you can find them again.
Now -- here are several websites that will help you learn to write "cause and effect":
1. Choose the speech from Act IV you want to use. Read it thoroughly so you understand it, backwards and forwards.
2. What was the cause of this? That is, what brought the speaker to the point of saying all this? What does the character say, in detail? What are the results of this speech?