There is something I need to tell you. There are two ways to say there is in English. But in French...
there is
il y a
there are
il y a
That's right! There's only one way to say it, which makes things nice and easy. A direct transliteration of il y a would be something like it there has, but never mind that.
Il y a une femme.
There is a woman.
Il y a des femmes.
There are women.
Wow, that's great! I like it simple.
Easy, right? It turns out that there's one slightly tricky bit with there isn't, there aren't (the negation).
I knew there was a catch...
The first thing to note is that we have to negate the verb a with ne ... pas as usual.
there isn't / aren't → il n'y a pas
That looks really complicated.
Don't worry. I suggest you just say this over and over: "Ilnyapah".
Ilnyapah... That's not so bad! I'll get started: il n'y a pas, il n'y a pas...
The second thing is that no matter what comes next (une, un, des, 3, etc.) you will have to replace it by de.
Il n'y a pas de femme.
There isn't any women/There are no women.
Let's play a game to practice. You have to negate everything I say: Il y a un canapé dans le bureau.
Il n'y a pas de canapé dans le bureau.
Il y a une guitare dans la chambre.
Il n'y a pas de guitare dans la chambre.
Il y a des plantes dans la maison.
Il n'y a pas de plantes dans la maison.
Bravo! I think you've got the hang of it already!
In less formal speech
In English we can say there's. In informal French, il y a might be pronounced more like y'a and il n'y a pas more like y'a pas.
Y'a un bus. → There's a bus.
Y'a pas de bus. → There's no bus.
These shortcuts are common when people are talking less formally in all languages, in the same way that want to sounds like wanna in English. Keeping your eyes (and ears!) open for these shortcuts is the key to understanding spoken French.