If you happen to have /home on a separate partition already (/dev/sda5 in this example), then it's a really easy process.
Do the following as the root user:
Install the cryptsetup package:
apt install cryptsetup
Copy your home directory to a temporary directory on a different partition:
mkdir /homebackup
cp -a /home/* /homebackup
Encrypt your home partition:
umount /home
cryptsetup -h sha512 -c aes-xts-plain64 -s 512 luksFormat /dev/sda5
cryptsetup luksOpen /dev/sda5 chome
mkfs.ext4 -m 0 /dev/mapper/chome
Add this line to /etc/crypttab:
chome /dev/sda5 none luks,timeout=30
Set the home partition to this in /etc/fstab (replacing the original home partition line):
/dev/mapper/chome /home ext4 nodev,nosuid,noatime 0 2
Copy your home data back into the encrypted partition:
mount /home
cp -a /homebackup/* /home
rm -rf /homebackup
That's it. Next time you boot your laptop, you will be prompted for the passphrase you set in Step 2.