PODER, QUERER and DEBER are three very useful verbs. These verbs allow us to say I am able to do something – I want to do something – I ought to do something.
PUEDO + infinitive e.g. puedo cantar – I am able to sing.
QUIERO + infinitive e.g. quiero cantar – I want to sing
DEBO + infinitive e.g. debo cantar – I ought to sing