How are affect and effect different?

The main difference is the part-of-speech.

To "affect" (transitive verb) someone or something is to influence them or it, or to create, bring about, or cause some reaction or change.

• "The loss of Mary's husband deeply affected Mary."
• "Global warming is affected by industrial pollution."

"Effect" is a noun. It is a result, reaction, or change caused by something.

• "The loss of Mary's husband had a deep effect on Mary."
• "Global warming is the effect of industrial pollution."