Affect, used as a verb means to have an influence on or to make a change in. Affect, used as a noun, describes a feeling or emotion.
Effect means to bring about, to initiate.
Usage:
Affect and effect seem to be close in meaning, but there are significant differences.
Affect means to influence. Thus, "Storage in a high temperature and high humidity environment will negatively Affect the food." [The food already exists. Storing it in a high temperature and high humidity environment will probably cause damage to the existing food.]
Effect means to bring about or cause. "If we are to raise enough food to feed ourselves this year, we must Effect changes in our spring planting." [We must change the previous way we planted in order to raise more food.]
Affect may be used as a transitive verb. The forms are Affected, Affecting, Affects.
Affect may mean to have an influence on. "The increase in earnings will affect the stock price."
Affect may mean to act on the emotions of. To touch or move. "The sight of his ex-wife with another man had its affect on him."
Affect may mean to attack or infect, perhaps as a disease. "If a woman contracts rubella during pregnancy, it may affect the development of the unborn child."
Affect may be used as a noun.
Affect may mean a feeling or emotion, especially as manifested by facial expression or body language. "The politician's voice and stance were carefully chosen to have a bland affect."
Understanding of the verb Affect is clearer when the relationship of Affect to its synonyms is seen.
"Your information will Affect my vote."
"Your information will influence my vote."
"The man's resume affected my thought to offer him a job."
"The man's resume impressed me and I offered him a job."
"The performance of that song always affects me."
"The performance of that song always touches me."