Ganas can perhaps best be translated as desire, or the urge to do something.
To run you only need legs, time and desire
Everything else is an accesory
Now that we know what ganas are we can start to talk about expressions like "Tener ganas de".
I feel like going to the movies
¿Tienes ganas de ir a la playa?
Do you feel like going to the beach?
No tengo ganas de ir al cine
I don't feel like going to the movies
You can use the expression tener ganas to express your desire to do anything, or nothing at all:
Hoy no tengo ganas de hacer nada
I don't feel like doing anything today
You can also say something like...
Se me pasaron las ganas
I don't feel like it anymore
There's also "dar ganas de". This is when something makes you feel like doing something.
Esta canción me da ganas de bailar
This song makes me want to dance
You may have also heard....
Which translates to something like "do your best", "put your all into it", "give it your best shot".
Give it your best Manuel, You can do it!!
There's also con ganas de.
Con ganas de verte
How are you?
With the urge/desire to see you / I really want to you see.
That loses a little something in the translation, but I think you get the picture. Once you get a good grasp on this subject, the Spanish will make much more sense.
I woke up today wanting to see you
And now we're about to get what I found to be an interesting and somewhat surprising use of the word ganas.
When you start talking about "las ganas", it's a way of refering to "deseo sexual" - sexual desire, or as we might say "to be in the mood". I wouldn't call that a literal translation, but it definitely conveys the meaning.
Es dificil no sentir ganas al verlo
It's hard not to be in the mode when you see him
Se perdío las ganas
He's not in the mood any more
Mi esposo tiene más ganas que yo
My husbands is in the mood more often than me
And finally, if you're with that someone special and the time is right, you can ask:
Are you in the mood?
Las ganas doesn't always refer to romantic urges, but the context will certainly make it clear when it does.
This post is by no means an exhaustive discussion of the word ganas and it's associated expressions, but it's more than enough to get you started.
¡Hasta la próxima!