The conditional tense is used to describe what someone would do or what would happen in the future. It can also be used to express ambitions and intentions. For example:
The most common verb in the conditional tense is me gustaría (I would like). This can be used to say what you would like to do in the future, eg me gustaría vivir en Nueva York (I would like to live in New York) or it can also be used for polite requests, eg me gustaría hablar con el jefe (I would like to speak to the boss).
The verb poder (to be able) can be used in the conditional to make the polite request or statement 'Could...?' For example, ¿Podrías prestarme un bolígrafo? (Could you lend me a pen?), la visita podría ser interesante (the visit could be interesting).
The conditional of the verb deber is used to mean should, eg debería beber más agua (I should drink more water), los profesores deberían ser menos estrictos (the teachers should be less strict).
The conditional is often used to say what would happen if something else occurred. This is formed using si (if) and the imperfect subjunctive. This is a complex structure, but it can be useful to learn a few set phrases containing it, eg:
The imperfect of hay (there is/there are) is había (there was/there were/there used to be). Había is useful for describing things in the past, eg: en mi pueblo había un restaurante (in my village, there used to be a restaurant).