Your funds are stored in the blockchain. And your wallet owns the key signatures to access those funds in the blockchain and claim them into your wallet.
It is quite important to password protect your wallet before doing a backup of it. This procedure is already explained in another article.
To backup your wallet file containing your key please follow these steps:
1) Open "File" menu. Click on "Backup Wallet"
2) Select the destination where to store your "wallet.dat" file. Select a safe place for example and external harddrive or pendriove.
If you ever lose this file, you won't be able to unlock your wallet and claim back your funds. We cannot help you on this. It's your responsability.
If you have "Automint" set to ON in the options, you need to backup your wallet everytime your get a new conversion of funds into "zLAX"
Means whenever you convert manually or by automint LAX to zLAX, YOU NEED TO BACKUP YOUR WALLET.