In Spanish, some verbs change their roots or endings in unpredictable ways. These verbs are called irregular because they do not follow the regular conjugation pattern. Mastering their common forms allows you to speak and understand more accurately.

"Ser" is used for identity, characteristics, and time. "Estar" is used for states, location, and results. Both are irregular and change a lot in present, preterite, and participle.

Have expresses possession, age, obligation, and sensations. It is irregular in the present indicative, preterite, and future, and its participle is regular. It also forms fixed expressions with 'tener que' for obligation.

"Ir" indicates movement, directions, and plans with "a". It is highly irregular in present and preterite. It is used with "a + infinitive" to talk about intention or near future.

Haber is used as an auxiliary to form compound tenses and as an impersonal ("hay") for existence. It is irregular in present, preterite and future as an auxiliary. "Hay" is the most common form to express "there is" or "there are".

Do expresses actions, creation, weather, and time elapsed. It is irregular in present, preterite, and future. Its participle may be irregular in very formal or archaic uses, but 'hecho' is the standard form.

Say is used to communicate, report, and order. It is irregular in present, preterite and future. In present, the irregularity is strongest in the first person singular and in preterite the root changes.

Poder expresses ability, permission and possibility. It is irregular in present (vowel change) and in future and conditional (short root). In preterite, the root changes and the endings are irregular.

Put means to place or situate and is used in many idiomatic expressions. It is irregular in the first person present, in the preterite and in the future. Its participle 'puesto' is irregular and very frequent in passive voice and compound tenses.

Come indicates movement toward the speaker or the reference point. It is irregular in present, preterite and future. It resembles "tener" in some forms of present and future.

Want expresses desire, intention, and affection. It is irregular in present due to vowel change and in future due to short root. In preterite, the root changes and it usually means attempt or a specific decision.

See means to perceive with sight and, by extension, to notice or verify. It is irregular in the preterite and imperfect, and its participle "visto" is irregular and very common in compound tenses. In the present, the irregularity concentrates in the first person singular.

The most common irregular verbs have their own changes in present, preterite, future and participle. Memorizing their key forms helps form correct phrases and better understand spoken and written Spanish.