Hi,
How do i know if the custom rom i m looking is RFS supported or EXT supported ?
And do every custom rom has its own kernel ? How do i know it has custom kernel built in
Welcome to the forum inwell!
You're not giving us much to work with, but as a general rule regarding what is or isn't supported in a particular rom, the developer of that rom will post this type of information in their original post (or changelog if you will)
As for the kernel, again it depends on the rom. The rom will often include the kernel with the rom download. If there is a separate or custom kernel required, the developer will post that in their original post and inform you to flash it separately. As with all roms, make sure said rom is compatible with your particular model and to follow all directions to the letter.
Good luck!