¿Cuándo se utiliza el pretérito perfecto, el imperfecto y el pretérito? = When do you use the perfect, the imperfect and the indicative past?

Firstly, let's start with the 'imperfecto' tense as it's the easiest to differentiate. The endings for this tense are as follows:

For regular verbs ending -AR in the infinitive (that is the 'to ...', e.g. to speak is hablAR), drop the AR and substitute the endings depending on the person with: -aba, -abas, -aba, -ábamos, -abais, -aban. 

For regular verbs ending -ER or -IR in the infinitive (e.g. comeER or vivIR), drop the ER/IR and substitute the endings depending on the person with: -ía, -ías, -ía, -íamos, -íais, ían. 

As always there are irregular verbs for this tense and it does include the usual culprits, amongst others- ser, tener and ir but we'll cover those later.

This tense is used for: a habitual or repeated action in the past (something you used to do often), an ongoing action in the past with no specified completion time (e.g. I was eating an apple), for the description of a scene of how things were happening when there was an interruption (e.g. I was eating breakfast when...) or general description of the past (e.g. I was afraid of bees/ It was 5am). So, to help you, generally think of this tense as the english 'i was' or 'i used to'. 

Phrases that commonly elicit the imperfect past are: 'normalmente, de vez en cuando, antes, todos los dïas, los lunes' but of course there are more that are a little less common too. 

Therefore, since the imperfect is used for the distant past, we now move on to the less distant past- we'll continue to go in order of furthest away in time to most recent past.

Next we have the 'pretérito' past. This is the past we most tend to think of when we think of the past in English, i.e. 'I went, I ate, I spoke'. The endings for this tense are as follows: 

For regular verbs ending -AR in the infinitive (e.g. to speak- hablAR), drop the AR and substitute the endings depending on the person with: -é, -aste, -ó, -amos, -asteis, -aron.

For regular verbs ending -ER or -IR in the infinitive (e.g. comeER or vivIR), drop the ER/IR and substitute the endings depending on the person with: -í, -iste, -ió, -imos, -isteis, -ieron.

This tense indicates a single event that happened (e.g. Visité unos museos- I visited some museums), an event that occurred, interrupting another action (... when the robber broke in) or changes in an existing physical or mental state in a specific moment (I was sacred when I saw the dog). 

Phrases that elicit this tense include: 'una vez, muchas veces, ayer, un día, el lunes, de repente, el mes pasado, la semana pasada' amongst others.

Finally- the 'pretérito perfecto'. This tense is a little harder to differentiate from the previous tense but there are differences in their uses. In english, it usually translates as 'I have gone, I have spoken, I have eaten'. It is generally related to the present because it happens in the same unit of time you are in Therefore phrases that elicit this tense include 'hoy, esta semana, este mes'. 

However, this tense is also used for other 'este' ohrases like 'esta mañana, este fin de semana' because though that time period is finished, the speaker is close to that moment or thier intention is to make it closer. e.g. Este fin de semana no he salido. 

Another use of this tense, similar to in English, is when we imply 'ever' or 'in your life'. For example: Have you ever been to Madrid? = ¿Has estado alguna vez en Madrid?

To form this tense, first we use the present tense of the verb 'haber': he, has, ha, hemos, habéis, han. This is then followed by the past participle of the verb:

-AR verbs subsitute the 'ar' with 'ado'

-ER and -IR verbs sibsitute the respective 'er' and 'ir' with 'ido'. 

Do you have any questions? If not, let's find an excercise where you can practice differenitating between the tenses so I can see that you'ce fully grasped the concept.