Using indexes to speed up queries

[DNCL]

Hello, i want to use indexes in mysql tables to speed up queries, can you give me the exact command to execute?


EDIT: found a command like this CREATE INDEX pagetext ON vb_post (pagetext);
but when i execute it i get the following error:
#1170 - BLOB/TEXT column 'pagetext' used in key specification without a key length
This is happening only in pagetext field in the whole table, other fields can be indexed, how do i fix this?

any help is appreciated