One helpful way to see cause and effect is to look for "clue word" such as and, because, and so.
For example
Tim forgot his math book, so he was unable to complete his homework.
The word so signals the cause and effect relationship. The part of the sentence before the word so is the cause, and the part of the sentence after so is the effect.
Kelly studied her spelling words and she got an A on the test.
The word and signals the cause and effect relationship. The part of the sentence before and is the cause, and the part of the sentence after and is the effect.
The signal word because is a little different....
Keegan was hungry because he skipped lunch.
The word because signals the cause and effect relationship. The part of the sentence before because is the effect, and the part of the sentence after because is the cause.