you can search for any ready made spell checked available else where.
You won't be able to do it alone with php unless you have a huge database of the words, against which you can check your spellings.

Yea, whatever you do, you will need a list of correctly spelled words to test against. PHP has no way to determine what is and is not incorrectly spelled unless it has something to compare it to.

Once you have that list, however, PHP has a few functions you can use to "guess" the correct word. Like the levenshtein function. (See the example there)

I have massive database of spelling words, dictionaries and grammar queries..

Is there no match like and replace type thing I can do?

If search.php action is..

$get request [q]

sql = select * all from products where q="request query form q" and match with spellinglist where word is like "request query form q" and like "spellinglist" suggestion

yes, you got it right. But if the spelling is wrong , say the user is searching for "camel"
and he types "camal: then your code need to do this too.
query should include...."..like '%cam[single char]l' " etc
or "..like '%cam%' " etc.
In short you will need to experiment with the wild cards little bit

Is there any way to do via an array.

I actually want to scan a html document source code and try to find spelling mistakes in it..

see if this is useful for you,
and

Thanks. I tried spellr.us.. that seems to be the best - I want to scan thousands of pages though.. and I want to do it myself free..

Like some mentioned, you'll need to decide on your options.
Also you'll need to ensure that punctuation marks are not included
in your words to check. It's possible that some words will have numbers in them (e.g. chemicals), so you may want to include words that have numbers in them, but not numbers by themselves.

If you get a 'nomatch', you'll then need to trawl for a series of wildcarded options and list them alphabetically.

You could use an autosuggest (ajax) list, although a MASSIVE db may slow down this function.