how do i make my own custom error/ 404 page?

http://www.lissaexplains.com/html6.shtml#error

Love,
Mirna

thanks. i should really search the site first :)

i made the .htaccess file, but is it supposed to be in .txt mode?

No, it shouldn't have the .txt or any other extension... just rename it in Notepad as ".htaccess" (with quotes) or upload it and rename in your FTP program.