Summarize:

The "passé composé" is for actions that had a definite beginning and end, such as "I threw a ball," or "They have baked a cake." Actions in the past that happen often or habitually (like the weather or your mood) use a different tense. The passé composé is the most common past tense in French. The passé compose is a compound tense, which is a fancy way of saying it has two parts. The first part is a conjugated version of "avoir" (to have)." This is similar to English, where you can say "I have eaten," or "She has run." This is the first part of your conjugation. As a refresher, the conjugation of "avoir" is:  Avoir (to have): J'ai, tu as, il a, nous avons, vous avez, elles ont. Think of the English expression, "I have eaten." Notice how "eaten" is not like any other conjugation for the verb "to eat." French does the same thing -- there is a different ending for the past tense of verbs. Luckily, they are easy to remember:   -Er verbs, "-é." Examples: parlé, montré, decidé.  -Ir verbs, "-i." Examples: fini, réussi.  -Re verbs, "-u" Examples: entendu, répondu. Simply add your conjugation of "avoir" to your past participle to form the past tense. While the literal translation will always be "I have talked," or "they have listened," this tense can also translate to "I talked," or "they listened." Several examples from different verbs:   First person: "ai + verb." J'ai parlé → I talked.   Second person: "as + verb." Tu as fini → You finished.   Third person: "a + verb." Il a entendu → He heard.   Plural first person: "avons + verb." Nous avons réussi → We succeeded.   Plural second person: "avez + verb." Vous avez essayé → You all tried.   Plural third person: "-ont + verb." Elles ont répondu → They responded. " The formula "avoir + past participle works for 95% of French verbs. However, there are a selection of verbs that must use "être + past participle" (to be) to be put in the simple past tense. The translation is still in the past ("I fell"). These verbs are:  Devenir, Revenir, Monter, Rester, Sortir, Venir, Aller, Naître, Descendre, Entrer, Rentrer, Tomber, Retourner, Arriver, Mourir, Partir A helpful way to remember these verbs is by the acronym, Dr. & Mrs. Vandertramp. You'll notice the list above is already in this order. Grammatically, these verbs are known as "intransitive verbs." & Mrs. Vandertramp verbs. Once you remember which verbs need "être" (to be), add the past participle to make the past tense. Note, however, that the verb has to match the subject. Plural phrases get an "-s" and expressions about females get an extra "-e"   First person: "suis + verb." Je suis tombée → I fell. ("I" refers to a woman.)  Second person: "es + verb."  Tu es tombé → You fell.   Third person: "est + verb." Il est tombé → He fell.   Plural first person: "sommes + verb." Nous sommes tombés → We fell.   Plural second person: "etes + verb." Vous êtes tombés → You all fell.   Plural third person: "sont + verb." Elles sont tombées → They fell.
Use the past tense for simple, complete actions in the past. Conjugate the present tense of "avoir" to start the passé composé. Find the "past participle" of your verb. Put the two parts together to form the past tense. Know the verbs that conjugate with "être" instead of "avoir. Replace "avoir" with "être" for Dr.