Both affect and effect can be used as nouns or as verbs, though affect is most commonly used as a verb (to act upon or influence). The effect is the result produced.
(verb): Will the drought affect the price of food?
The disorder affected his ability to perform his job.
The loss affected her deeply.
(noun) (Note that the pronunciation differs when affect refers to an emotional or psychological state): Blunted affect is often a sign of depression.
(noun): The effect of the drug was immediate.
Many drugs have side effects.
The special effects were spectacular!
The law will go into effect next year.
A tornado watch is in effect until midnight.
(verb): Therapy is designed to effect change.
(adjective): Apply the ointment to the affected area.
Her kindness is sincere, not affected.
(This last use is similar to affectation (noun): Her affectations fooled no one.)
(adjective): The new policy is effective immediately.
His methods are effective.