Vamos sair para o pátio, onde o sinal é mais forte.

In Portuguese vamos is the 1st-person-plural present of ir. When you attach an infinitive (here sair), it forms a periphrasis that can express either:
• A suggestion or invitation (“Let’s go out…”).
• A near future (“We’re going to go out…”).
In this sentence it works as “Let’s go out…”.

Both are possible:
– Vamos ao pátio uses the preposition a + article o (contracted as ao) to indicate destination (“We’re going to the patio”).
– Vamos para o pátio uses para to stress direction or goal.
– Sair para o pátio adds sair to highlight exiting an indoor space.
All three convey a similar idea; the nuance is in whether you stress the act of leaving (sair) or just the destination (ir a/para).

Portuguese generally uses definite articles before singular countable nouns when talking about a specific place or thing.
– o pátio means “the patio.”
Omitting the article (vamos a pátio) sounds unnatural. You could use an indefinite article (um pátio) if you meant “some patio,” but here it’s a known/shared patio, so you need o.

Onde is the relative pronoun for a place where something is or happens (static location).
Aonde is used with verbs of movement toward a place (e.g., aonde vais? “where are you going?”).
Here you’re describing the location where the signal is stronger, not movement toward it, so you use onde.

Mais forte is the comparative form (“stronger”). In Portuguese you can explicitly compare with do que (“than”), e.g. o sinal é mais forte do que aqui.
In a relative clause introduced by onde, the do que + reference (aqui) is often omitted because it’s implied by the contrast between places.