HI!
So i make a new address on my Electrum wallet. And the just use the seed i get in Electrum and then use it in ElectronCash wallet?
Why cant i use the seed that i received long time ago when i made my Electrum wallet for the first time?
You can... what Lucius was suggesting is that you create a new seed with new addresses in Electrum and move all your BTC from your old seed (and old addresses) to a new address on the new seed.
Then you simply import the OLD seed into Electron Cash and you can get your BCH without worrying, as all the BTC has already been moved... so your BTC is safe, even if ElectronCash is compromised and you put your OLD seed into it... you only stand to lose your BCH (and BTG and other Bitcoin Forks)
To make sure you don't do anything stupid...
1. Don't do this when you've been drinking!
2. Get Electron Cash from official site:
https://electroncash.org/#download3. Take the time to verify the download using digital signatures (preferred) and/or file checksum/hashes (not as safe) as outlined here:
https://github.com/fyookball/keys-n-hashes4. Don't rush