Tenses

ar verbs
	present	future	imperfect	past definite
1st singular	-o	-é	-aba	-é
2nd singular	-as	-ás	-abas	-aste
3rd singular	-a	-ás	-aba	-ó
1st plural	-amos	-emos	-amos	-amos
2nd plural	-áis	-éis	-ais	-asteis
3rd plural	-an	-án	-an	-aron

er and ir verbs
	present	future	imperfect	past definite
1st singular	-o	-é	-ía	-í
2nd singular	-es	-ás	-ías	-iste
3rd singular	-e	-ás	-ía	-ío
1st plural	-emos/-imos	-emos	-íamos	-imos
2nd plural	-éis	-éis	-íais	-isteis
3rd plural	-en	-án	-ían	-ieron

Tense	Used for
Present Indicative	action at the present time a state of being a habitual action an occurrence in the near future a past action that contines up to the present
Imperfect	habitual or repeated action in the past people, things, or conditions of the past e.g., he hallado - I have found
Pluperfect	used to refer to an event that has completed before another past action e.g., hacía hallado -I had found
Past Definite	a single complete action in the past not descriptive carries a narrative forward

In English the present is subdivided into the following forms:

Present simple: "I go to school every day."
Present progressive: "You are being rude." (at this moment)
Present perfect: "I have had two computers."
Present perfect progressive: "She has been living in London for a year."

The imperfect, also known as the past progressive, is often used in was and used to forms, as in:

I was eating.
I used to eat.

The imperfect is formed with the present tense of haber plus the past participle of the verb. The pluperfect is formed with the imperfect tense of haber plus the past participle of the verb.

The Past Definite, aka, the preterite, is used in Spanish for a complete single action, wholly over, e.g.,

Napoleon died in 1821
The man killed the dog

It is generally formed by adding -ed or -d to the verb's plain form.