how to chek the integrity of dowloded iso ,pls explain in a step by step
thanks

Checksum file is necessary. Easiest way is to use Downthemall with Firefox and cut and past the checksum provided from the ISO download site into the window box provided prior to download.
Post-download, use the command in terminal (example is for MD5sum)SHA256sum and other checksums are or should be available, too.

Here is an in depth rurorial on how to check the md5sums of a Linux iso download or a CD that you have burned to disc. It also has instructions on how to check md5sums from Mac OS X or from Windows:
https://help.ubuntu.com/community/HowToMD5SUM
When you burn your downloaded iso to a CD or DVD, be sure to burn it at the slowest possible speed to avoid errors.
If you use Ubuntu (or Kubuntu, Xubuntu, or Lubuntu) you can just hit the space bar when the CD or DVD boots up and choose to "check the CD for defects". This will check the disc to be sure that there are no errors.

Write back if you need more help.
And welcome to the LQ forums!

sarko
you are going to have to post A LOT and i mean A LOT more details than only
we will point you in the right direction
BUT WE WILL NOT DO YOUR WORK FOR YOU !!!!

also SPELL out your words !!!
PLEASE IS NOT SPELLED AS "pls"

this is NOT a text message on a phone !
so please DO NOT treat it as such !