If you imported it in electrum, it should be extremely straightforward to make a transaction, and shouldn't be any different then how you would normally do it.
making a raw transaction with imported private keys should also be the exact same, and not any different as to how you would normally do it. (?)
I don't have electrum account so I don't know how private keys can be used to transfer from my imported to my main address without paying fees. Can anybody explain?
You can't. You will need to pay a network fee if you want to get the balance from the imported wallet on your "Main" wallet, as i explained above.
(You can ofcourse choose to not include a fee, but chances are highly unlikely that your transaction will be confirmed anytime soon).
Private keys are simply the "keychain" to your bitcoin. It is not some magical network fee remover.
I have my bitcoin account on blockchain sence 1 month and I have about 0.007BTC in main account and 0.015 in imported address.
All I want to do is transfer from imported to main address. I tryied many ways and it shows me always 41$ to make transaction.
I 'm a newbie in bitcoin account so I don't know even how to start. anyone can guide me and help me in first steps on how private keys can be used?
With the current state of the mempool, I'd say that unfortunately that fee is quite reasonable if you want to get your transaction confirmed anytime soon.
This would be a transaction similiar to yours.
https://blockchain.info/tx/84c978301cf722947ed4461055d38876dc024862cf04b4a05b3e01d9db30f264Why do you want to sweep everything into 1 adress anyway?