Hi jLim

Affect, Effect

Generally, 'affect' is a verb, 'effect' is a noun

• The effects of Japan's tsunami can still be seen in many coastal areas.  (Effect = noun)
• The tsunami affected hundreds of thousands of people. (Affect =  verb. Think of the letter 'a' -  a for action, a for affect as a verb)

Impact 

Don't use impact as a verb. It's too new. Just use it as a noun. Use 'on' with it

• The election had a huge impact on the country.

Influence

Influence can be a noun or a verb. Use 'on' with influence as a noun.

• The English language is influenced by French. 
• My uncle influenced me. 
• Italian society is trying to fight the influence of criminal groups such as the Camorra or the Cosa Nostra.
• Michael Jackson had a huge influence on pop music.