أَنْ joins an imperfect verb and makes the complete expression carry verbal-noun meaning.
Example: أُحِبُّ أَنْ أَقْرَأَ means “I like to read.” The words أَنْ أَقْرَأَ together express the idea of “reading.”
Do not call أَنْ alone a verbal noun. The meaning belongs to the whole combination أَنْ + فعل مضارع.