do
The Spanish word 'do' does not directly translate to 'do' in English. Depending on the context, 'do' in Spanish could be an abbreviation for 'Domingo', which means 'Sunday'. A direct translation or equivalent for 'do' as an action verb in English does not exist in Spanish. Spanish verbs are usually in the form of 'hacer', 'hago', etc. depending on the tense and pronoun used.
What should I do?
This is a sentence asking for advice or instruction, using the verb 'debo' which is the first person singular form of the Spanish verb 'deber' (should) followed by the infinitive verb 'hacer' (do).
I will do it later.
This is a statement expressing the intention to perform an action in the future, using 'haré' which is the first person singular future tense of the verb 'hacer' (do).
He/she did his/her job well.
This is a statement expressing a past action done proficiently, using 'hizo' which is the third person singular past tense of the verb 'hacer' (do).