Article: Remove the -ir ending from the infinitive and replace it with the appropriate ending to talk about present actions. The -ir endings are -o, -es, -e, -imos, is, and -en. For example: Yo abro: I open. Tu abres: You [informal] open. El/ella/usted abre: He/she opens; you [formal] open. Nosotros abrimos: We open. Vosotros abris: You all [informal] open. Ellos/ellas/ustedes abren: They/you all [formal] open. When you're discussing an action that doesn't extend at all into the present, the preterite tense is appropriate. Depending on your subject pronoun, you will replace the -ir with -i, -iste, -io, -imos, -isteis, or -ieron. Yo abri: I opened. Tu abriste: You [informal] opened. El/ella/usted abrio: He/she/you [formal] opened. Nosotros abrimos: We opened. Vosotros abristeis: You all [informal] opened. Ellos/ellas/ustedes abrieron: They/you all [formal] opened. When you're talking about something that happens habitually, or that was interrupted, conjugate your verb in the imperfect tense. For an -ir verb, this means replacing the -ir with -ia, ias, ia, -iamos, iais, or -ian. Yo abria: I was opening. Tu abrias: You [informal] were opening. El/ella/usted abria: He/she was opening; you [formal] were opening. Nosotros abriamos: We were opening. Vosotros abriais: You all [informal] were opening. Ellos/ellas/ustedes abrian: They/you all [formal] were opening. In Spanish, the conditional tense is used to describe actions that might happen, or that are dependent on some other condition to happen. Regular -ir verbs are conjugated using the same endings as the imperfect tense, added to the end of the infinitive rather than the verb stem. Yo abriria: I would open [if]. Tu abririas: You [informal] would open [if]. El/ella/usted abriria: He/she/you [formal] would open [if]. Nosotros abririamos: We would open [if]. Vosotros abririais: You all [informal] would open [if]. Ellos/ellas/ustedes abririan: They/you all [formal] would open [if]. Add an ending to the full infinitive to conjugate regular -ir verbs in future tense, just as you did with the conditional tense. Use the endings -e, -as, -a, -emos, -eis, and -an. Yo abrire: I will open. Tu abriras: You [informal] will open. El/ella/usted abrira: He/she/you [formal] will open. Nosotros abriremos: We will open. Vosotros abrireis: You all [informal] will open. Ellos/ellas/ustedes abriran: They/you all [formal] will open.

What is a summary?
Use the present tense to describe actions currently happening. Switch to the preterite tense if the action happened in the past. Move to the imperfect tense if a past action continues to happen. Add the imperfect ending to the infinitive to express the conditional tense. Pick the future tense for talking about actions that will happen.