‘Take care’ is usually used to say goodbye to someone and it means to stay safe. It is a short version of ‘take care of yourself’.
A: I’m leaving on my trip!
B: Take care! Don’t forget to send me a postcard!
However, when we use the full phrase we must remember ‘of’! If you forget it then the form of the word will be incorrect.
I can’t go out tonight because I need to stay home and take care of my sister. (Correct!)
I can’t go out tonight because I need to stay home and take care my sister. (Incorrect)