Why Electrum has 20 receiving addresses and 6 change addresses?

[Pmalek]

I don't have verified the signature, what is it?

It is important to verify the signatures to make sure that the version you have downloaded belongs to the right developer, in this case to ThomasV.

Follow this guide posted here on Bitcointalk > https://bitcointalk.org/index.php?topic=4183993.0
Or use this > https://bitcoinelectrum.com/how-to-verify-your-electrum-download/