Function

The conditional mood in Portuguese is the equivalent of the "would + infinitive" construction in English.

It is used to express a situation in which there are "conditions". For example:

I would go to the party if you took me.
Eu iria à festa se você me levasse

The conditional is frequently used along with the imperfect subjunctive, as in the context above.

conditional + if + imp. subjunctive - Eu compraria um carro se tivesse dinheiro.

If + imp. subjunctive + conditional - Se eu tivesse dinheiro, compraria um carro.

It is also used with the verb gostar. For example:

Eu gostaria ir ao centro. - I would like to go into town.

Also note that the first person plural contains an accent over the last "i".

Gostaríamos ir ao centro se você chegasse também.

Edit

Formation

In regular verbs, the conditional is formed by adding these never-changing endings to the infinitive.

FALAR - to speak

I would speak	Eu falar	ia
You (s,inf) would speak	Tu falar	ias
He would speak (also ela, você)	Ele falar	ia
We would speak	Nós falar	íamos
You (p) would speak	Vós falar	íeis
They would speak (also elas, vocês)	Eles falar	iam