"The girls have dresses."
Translation:Les filles ont des robes.
There are two different verbs here: être (to be) and avoir (to have)
The pronouns take different forms of the verb.
je suis = I am
tu es = you are (singular)
il/elle/on est = he/she/"one" is
nous sommes = we are
vous êtes = you are (plural)
ils/elles sont = they are
Above you can see the conjugation for avoir.
For items possessed, use avoir (to have). For hunger, thirst, pain, feeling cold or hot, use avoir. j'ai faim, j'ai froid*, etc.
For feelings, states of being (sick/healthy), and adjectives, use être (to be). The verb to use is not always the same as in English, but with time, you'll learn which verb to use with which idiomatic phrase.
You can also hear the difference in the way it is pronounced. The liaison between the final s in elles and the ont makes a Z sound, whereas the sont in elles sont is a hard S sound.
elles ont → el Zon
elles sont → el Son
Verb "to have" (avoir)
I have = j'ai
you have = tu as
he/she/it has = il/elle a
we have = nous avons
you have = vous avez
they have = ils/elles ont
Here is a conjugator to help you conjugate French verbs: http://la-conjugaison.nouvelobs.com/du/verbe/avoir.php
In French, the verbs are conjugated differently depending on the pronoun. Conjugation is much simpler in English so this is a difficult thing for French learners, but I promise that with time and practice it becomes easier.
Here is avoir "to have" conjugated:
j'ai → I have
tu as → you have
il/elle/on → he/she/"one" has
nous avons → we have
vous avez → you have
ils/elles ont → they have
You will notice that even in English the third person singular changes to "has," so conjugation exists in English too, it is just very minor. I recommend that you read the "Tips and Notes" on the web version of Duolingo. You will find a lot of helpful information there. Click on a skill and then click on the light bulb icon.
"Des" is the plural indefinite article in French. Un/une is the singular indefinite article. This plural indefinite article doesn't exist in English, so we don't usually write anything for the plural form in English. Occasionally we can write "some." This article is required in French.
une robe, des robes → a dress, dresses
un enfant, des enfants → a child, children