"That girl looks like a boy."
Translation:Cette fille ressemble à un garçon.
"ça" is a pronoun, meaning "that thing". You cannot use it as a determiner.
Cette is the feminine demonstrative adjective that means "that or this" and fille is a feminine noun meaning "girl" hence
"That girl ..." = Cette fille ....
Please why "Cette fille là ressemble à un garçon." is not accepted? And if we change "that" by "this" what would change in the translation?
« To look like » is not « to look at ».
To look like = ressembler à.
To look at = regarder.
That girl looks like a boy = cette fille ressemble à un garçon.
That girl looks at a boy = cette fille regarde un garçon.