To Enable disk encryption on your Windows:
To Enable disk encryption on your Mac:
In the Finder on your Mac, open a window, then Control-click the item you want to encrypt in the sidebar.
Choose Encrypt [item name] from the shortcut menu.
Create a password for the disk and click Encrypt Disk.
Important: Be sure to record and keep this password in a safe place. You cannot access the data on the encrypted disk without it.
It may take some time to encrypt, depending on how much information is stored on your Mac. However, you can use your Mac as usual while the disk is being encrypted.
Protect your Mac information with encryption – Apple Support (UK)
Remember to choose a strong password and keep it secure!