There are many words in the English language that have multiple spellings but are pronounced exactly the same. These words are not interchangeable -- each spelling has a distinct meaning. In conversation you don't need to have a command of these spelling differences, but in written communication misspelling the word can completely change the meaning of the sentence or simply render the sentence nonsensical.
These words are the reason you should never rely solely on the spell-check program on your computer. Words can be spelled perfectly and have a meaning that is completely wrong.
Below are several of the most commonly confused words that have more than one spelling -- and meaning. A periodic review of these will improve your writing in almost any situation.
Accept -- Acknowledging something with consent or to give approval.
There - Refers to a location.
Their - A plural possessive.
To - A preposition referring to a location (as in "They are going to town.)
Too - Means "also" or "very." It can be used to refer to an excess of something (too many people) or to indicate the addition of something (they will go too)
Forth -- Forward or onward. (The army went forth under the general's leadership.)
A tic is an involuntary muscle spasm (He had a nervous tic in his cheek.).
Discreet -- Meaning you can keep a secret. (Being discreet is essential for a therapist.)
Altar -- A place where you worship, usually in a religious setting.
Carrot -- An orange root vegetable
Caret -- an editor's mark used to indicate where text needs to be added.
Principal -- the first or primary of something. This has several meanings, such as the principal of a school ( the head of all other administrators); the principal owed on a loan (the primary amount before interest); or someone who is the principal member of a group (such as the actor playing the lead part in a production).
All ready -- Completely prepared for something. (The class had the project all ready before the due date.
Peace -- lack of war or conflict, calm. (There was peace for several years after the battle.)
Stationary -- Immovable or staying in one place. (The guard was stationary at his post for several hours.)
Cite -- To refer to something, usually in a scholarly paper. (She cited several magazine articles.)
Site -- A location (The site for the new building was chosen.)
Coarse -- Rough or uncouth (He had a coarse personality.)
Pour -- To dispense something, usually a liquid. Can also be used figuratively, such as pouring out advice.
Rain -- Precipitation (It rained for days.)
Rein -- Either the leather straps & bit used to guide a horse, or the act of (figuratively) using some similar means to slow someone down or keep them under control. (She tried to rein in her impulse to overeat.)
Compliment -- to praise someone with positive feedback (I complimented her on how pretty her eyes were.)
Metal -- Any of many materials such as iron, brass, steel and gold.
Affect -- Influence -- this is a verb. (She was affected by his coldness.)
Peaked -- Reached its summit or maximum. (Interest has peaked.)
Piqued -- To stimulate or excite. (The scent of barbeque piqued his appetite.)