You can set a password for your Electrum wallet by clicking the padlock symbol in the bottom right corner.
This can be a different password for each wallet. The password isn't just a barrier like the PIN of a bank card but the private keys actually are encrypted using it and AES-256-CBC (Source) which means that the password is needed to spend money. However, your transaction history, your own addresses (and therefore how much money you have) can be seen without knowing your password. This is the reason Electrum can give you this info (like your total balance) without requiring you to enter your password first.
If you want to back up your wallet, you can literally just do that because an Electrum wallet is just a single file.
The Electrum folder is
~/.electrum on Linux and Mac and described without slashes for Windows as
UsersYourUserNameAppDataRoamingElectrumwallets on the official Electrum website but you'll probably find it. In it, there is a folder named
wallets which is the default location for Electrum wallets. The wallets are text files which have the same name as the wallets.
Backing up the wallet files has the added advantage that you get your note-like data back (description of sent transactions, receiving notes, contacts). This obviously can't be generated from the seed because it's data entered by the user after the seed is set. However, it's written to your wallet file and if you copy it to a different computer (or the same computer later on after its hard drive exploded) you get the note-like data back.