Translation:I am not good at writing.
作文 means just an essay, while 文章 is more general and can also mean just "writing" or "sentence".
To be honest I've never heard 文章 used as "essay" while living in Japan. When my teachers or friends wanted to say "essay", they always used 作文. But that might just be a local thing and jisho says it can mean "essay", so it's probably fine.