For many languages, iPhone has dictionaries to help you type. The appropriate dictionary is activated automatically when you select a supported keyboard.
For a list of supported languages, see www.apple.com/iphone/specs.html.
iPhone uses the active dictionary to suggest corrections or complete the word you’re typing. You don’t need to interrupt your typing to accept the suggested word.

To reject the suggested word, finish typing the word as you want it, then tap the “x” to dismiss the suggestion before typing anything else. Each time you reject a suggestion for the same word, iPhone becomes more likely to accept your word.
To use the suggested word, type a space, punctuation mark, or return character.
Choose General > Keyboard and turn Auto-Correction on or off. Auto-Correction is on by default.
NOTE: If you’re entering Chinese or Japanese, tap one of the suggested alternatives.