thank you for quick reply, but i am still confused. when i click export i got 26 line electrum-private-keys.csv which contains "address, private key" like this (testing it so does not matter if this goes public):
address,private_key
1Cks4gBx5VsNJnzHUAPS8oVxRHeL795Wvq,KxCCniJif99E594mgomqrguc1ZUfDL5UbzXbanfWr732eGgHU6y4
13woCaMcUGhZZzU6SYsgYo7xDHvwxQAp7b,KydEuvT5qndyuk8Q1tYoeEoQqwfVQZqBULKiqqGgThUi1Ba5YUEm
and so on
it looks like electrum private keys for 26 bitcoin address. what is the use of rest of 25 address?
From memory... By default Electrum will generate 20 "receive" addresses... and 5 "change" addresses. Each time you receive funds to a "receive" address that has not been used before, Electrum will automatically generate another "receive" address to maintain this pool of 20 addresses. The same applies to "change" addresses... each time funds are sent to an unused change address, it will automatically generate another change address.
If you show the "addresses" tab in Electrum (Wallet -> Show Addresses)... you will be able to see all the addresses currently generated for your wallet (Note: you may need to expand the "used" and "change" sections by clicking on the ">" symbols.
So, you start with 20 receive + 5 change = 25 addresses... you used one to receive funds, so a new receive address was generated... you now have 21 receive and 5 change = 26 addresses.
The reason for having the pool of addresses is to help minimise address re-use... you can give a different address to each person/service you are requesting coins from. As new ones are only automatically generated when you actually receive a transaction to an address... having 20 spare means you will hopefully not run out before new ones are generated
