Good question, Juan. Almost all verbs are regular in the present, with the big exception of "to be," as well as other exceptions like "to have." ("Modal" verbs, such as "can" and "will" have their own peculiarities.) Generally, irregular verbs are those that do not form the past tense and past participle by simply adding "-ed." Examples of regular verbs: work / worked / worked, tie / tied / tied, listen / listened / listened. Examples of irregular verbs: give / gave / given, run / ran / run, teach / taught / taught. Irregular verbs include the most common verbs in the English language, so you should find a list of "common English irregular verbs" and learn them. Remember to start with the most common ones first (so start with a short list -- you can also find such a list in the back of your English textbook -- appropriate to your level. Have fun!