First of all, you have to download the wallet frow the electron-cash website. Here is the link http://www.electroncash.org/
Then press download and open the .exe file. You should get the electron-cash wallet window on your desktop.
Choose a name for your wallet and then click on 'next'.
Click on the wallet type you want to have. (Standard wallet is the quickest way, two factor authorization is safer).
'Next' again, then click on 'I already have a seed'.
Export your seed from your Bitcoin wallet and write in the blank space. If it is correct click on 'next' and you should see you BCASH on the electron-cash wallet.
NOTE: If you want to keep your Bitcoin safe, be sure to move your bitcoins from the old wallet to a new wallet AFTER having exported the seed from the old one and BEFORE pasting it on the electron-cash wallet. This should prevent electron-cash from using the seed you give them to steal your Bitcoins, as the wallet they would steal will be empty.
Hope this tutorial is clear enough, if you have questions write them in the comment section below!