CSS adding sidebars to dogcare template

hi!
i want to add side bars to dogcare template
https://freewebsitetemplates.com/preview/dogcare
https://freewebsitetemplates.com/download.php?template=dogcare

and i cant figure out what and where to write it on the css file..
every time i try the whole template crashes

what should i add to the code?

i want side bar from the left side and a side bar from the right side
in order to put small pictures in each of them

thanks!
joey