linux – Debian – How to create an image file .img of your current system as a backup

I am new to Linux Embedded, and I am now trying to make sure I back up my system before making changes. I intend to use dd if=/dev/sdX of=/destinationPath/backup.img to create the image file and save it to my 16GB sd card, so if something goes wrong, I can just reboot my device using the backup.img file.

My question is how to determine which partition should I use as the input sdX in the command line dd dd if=/dev/sdX of=/destinationPath/backup.img. Specifically, this is my system:

root@fun-shrimp:~# lsblk
NAME         MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
mmcblk0      179:0    0  7.3G  0 disk
├─mmcblk0p1  179:1    0  128M  0 part /boot
├─mmcblk0p2  179:2    0    1M  0 part
├─mmcblk0p3  179:3    0    2G  0 part /home
└─mmcblk0p4  179:4    0  5.1G  0 part /
mmcblk0boot0 179:32   0    4M  1 disk
mmcblk0boot1 179:64   0    4M  1 disk
mmcblk0rpmb  179:96   0    4M  0 disk
mmcblk1      179:128  0 14.9G  0 disk  <------ My 16GB SD card
└─mmcblk1p1  179:129  0 14.9G  0 part
root@fun-shrimp:~#

Also, is there anything I should be aware of when doing this?