Is there some trick, pattern, or a given grammatical structure that would tell me when i need to use the spanish word "a" in front of a verb's infinitive? like "voy a ir." why is the "a" needed?

If someone deletes this you will get a virus free

Fill in the blank with the correct form of preterite or imperfect of the verb in parentheses. nosotros a la playa con ana ayer. (ir) answer for blank 1:

Read and select the correct option for the blank. an exchange student from mexico brings a typical food from his culture to school. after you ask, what can he say? —hola, amigo fernando. yo como el ceviche. —¿eres de méxico? —sí, soy de méxico y come la tortilla escribo la yerba mate escribe la yerba mate como la tortilla