Most major applications have their own spell-checking features. OpenOffice's spell-checking feature can be accessed from the "Tools" menu inside OpenOffice. Firefox, Evolution, and many other GNOME applications will check your spelling as you type. Misspelled words will be indicated by a dotted red underline, and uou can right-click on those words to see suggested spellings.
To spell-check plain text files, you can use the ispell program. ispell is a command-line program, so it needs to be run in the Terminal window:
This will start ispell and check the entire file immediately.
When ispell finds a word that is not in its dictionary, it will outline the word in reverse video (highlighted). If there are "near misses" in the dictionary, ispell will also display the incorrect word and a list of correct alternatives at the top if they exist.
At this point, you can type one of the following characters:
|r||Replace Word||Ispell asks you for a replacement word. Ispell will not check the spelling of the replacement.|
|1, 2, etc...||Replace Word with suggested word||The suggested replacements at the top of the screen are numbered. If you type a word's number, ispell will use this word as a replacement.|
|<space>||Skips Word||Leave this word as is. If this word is encountered again, ispell will stop and prompt you for an action.|
|a||Accept Word||Accept this word as correct for remainder of ispell session|
|i||Add Word||Add this word to your personal dictionary. This is a file in your home directory called spell.words which tells ispell to accept the word as correct every time you use ispell (useful for things like your name).|
|<CTRL-G>||Quit Ispell||You can quit ispell at any time by pressing <CTRL-G>. This is done by holding down the CTRL key and pressing "G".|
The man page on ispell lists more options and gives more detailed information on this program.