I write my electrum private seed on the piece of paper and save it with me but i fear that someone near to me may read that paper and get access to the wallet. So i copied the wallet file on my usb and also write the seed in notepad in that usb. Now i want to password protect that usb or encrypt it so if anyone tries to access that usb, he can never open and read it contents. How to do this ?
You should be able to hide your paper backup of your Electrum mnemonic recovery words in such a way that only you can find it. But what if you forget your hiding spot? It would be a single point of failure.
USB flash devices can fail (happened to me), so don't rely on only one backup device!
You wrote your mnemonic recovery words on a computer that was likely online and with unknown security status. This should be avoided and you may consider your mnemonic recovery words as not safe anymore. (Depends on what daily internet "shit" you do on that computer.) Mnemonic recovery words of wallets should only treated on offline and non-digital devices like paper or metal backup.
You could use Veracrypt or Bitlocker or something similar and reliable. But again, don't do that with your mnemonic recovery words on a digital device that will go online any time later. Boot a live Linux that solely runs in RAM or TAILS, both have to stay offline, if you play with private keys and/or mnemonic recovery words, so that after shutdown none of your secret keys and words are retained on the used computer.