soñar
Soñar con is the key phrase. You dream 'with' something in Spanish, both when sleeping and when aspiring.
soñar con (sleep)
To dream while asleep. Always soñar con.
Anoche soñé contigo.
I dreamed about you last night.
Contigo, not 'de ti' or 'sobre ti'.
Sueño con volar.
I dream about flying.
Soñar con + noun or infinitive.
Tuve una pesadilla.
I had a nightmare.
Nightmares don't use soñar. 'Soñé una pesadilla' is rare.
soñar (aspire)
To dream of a future you want, or to daydream.
Sueña con ser actriz.
She dreams of becoming an actress.
Aspiration. Soñar con + infinitive.
Soñar es gratis.
Dreaming is free.
A common saying when someone is fantasising.
¡Ni lo sueñes!
Don't even think about it!
Ni soñarlo = no way. Informal refusal.
Tricky bit
Learners say 'soñé de ti' or 'soñé sobre ti' from English 'dream about'. Spanish uses 'con' every time. And 'sueño' is also 'sleepiness': 'tengo sueño' = I'm tired.