"It is my nice gray dress."
Translation:C'est ma jolie robe grise.
I also found this very helpful when trying to understand this:
Certain adjectives are placed before the noun, some of which you can memorize with the acronym "BAGS": Beauty, Age, Good and bad, Size (except for grand with people)
"sympa" is used in a very versatile way: that is a convenient adjective that works for anyone and anything.
- une idée sympa = une bonne idée, une idée séduisante (good, attractive)
- une voiture sympa = a nice car
- une fille / un garçon sympa = a friendly girl / boy
"Jolie" is used for a pretty girl but not for a handsome boy (un beau garçon)
This is a rule you will have to apply VERY often on Duolingo. In French, "c'est" (sing.) and "ce sont" (plural) are used in a large variety of expressions, when a pronoun (it, she, he, they) is subject of verb "être" and followed by a nominal group, ie: article (+ adjective) + noun.
- it is + nominal group => c'est
- she is + nominal group => c'est
- he is + nominal group => c'est
- they are + nominal group => ce sont
look here, there is a good explanation of this important and interesting rule : http://www.frenchtoday.com/blog/cest-versus-il-elle-est