Imperfecto subjunctive is used when main clause is imperfect, preterite, conditional, or pluperfect-

(Might ....... )

-er verb 

iera/iese

ieras/ieses

iera/iese

ie'ramos/ie'semos

ieran/iesen

Example-

comiera

comieras

comiera

comie'ramos

comierais

comieran

-ar verb

ara

aras

ara

áramos

aran

Present perfect Subjunctive

-consists of the present subjunctive of Haber plus a past participle

(May have)

-Espero que haya parado de llover para tres horas

Use when verb of main clause is in-

present indicative

present perfect

future command

Haya ...ado(ido)

hayas

haya

hayamos

hayáis

hayan

Pluperfect Subunctive- (might have ....)

-consists of the imperfect subunctive of Haber plus past participle

-No esperaba que hubieran llegado tan temprano

use when verb of main clause is in -

Imperfecto

Preterito

Conditional

Pluperfect

Present subjunctive- look, may look, eat, may eat (formal)

mira tú, no mires,come tú, no comes(informal)

mire

mires

mire

miremos

miréis

miren

coma

comas

coma

comamos

comáis

coman