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): Blunted affect is often a sign of depression.
(Note that the pronunciation differs when affect refers to an emotional or psychological state.)
(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.