The first way is less formal and can be used when speaking amongst friends. Remove the last syllable of the verb in its dictionary form and then simply add 'ta' or 'tta' to the end of the verb. For example, the verb 'taberu,' which means to eat, would become 'tabeta.' 'Watashi ha takoyaki wo tabeta' means I ate takoyaki. If you did not eat takoyaki, and need to say this in the past tense, you would again remove the last syllable from the verb, in this case, 'ru' and add 'nakatta.' The fragment 'nakatta' means that something did not happen. You could say, 'Watashi ha takoyaki wo tabenakatta,' meaning I did not eat takoyaki.