Deixis: ir/vir, levar/trazer

The short answer

Portuguese chooses the verb by looking at where the speaker is. Vir (come) and trazer (bring) move towards the speaker's place: Vem cá! (come here!), Traz um café pra mim? (bring me a coffee?). Ir (go) and levar (take) move anywhere else: Vou aí amanhã (I'll come over tomorrow), Vou levar um bolo pra festa (I'll take a cake to the party). That is why "I'm coming!", answering someone who calls you, is Já vou!

How to form it

Levar is regular. Vir and trazer are irregular in the present and the past, and ir you already know (vou, vai, vamos, vão; past fui, foi, fomos, foram).

Commands: spoken vem and traz, standard venha and traga. In the imperfeito, vinha is irregular; trazia and levava are regular.

When to use it

• vir: towards here, or towards where the speaker is talking from: Meus pais vieram de Teresina pra me ver. Você vem no meu aniversário?
• ir: anywhere else, including towards the person you are talking to: Já vou! Tô indo (I'm on my way). A gente foi pra praia.
• trazer: bring something here: Você trouxe o guarda-chuva? Moço, traz mais um guaraná?
• levar: take something or someone somewhere else: Sempre levo marmita pro trabalho. Você pode me levar na rodoviária?
• buscar: go and get, pick up: Vou te buscar no aeroporto. To look for something is procurar.

• Vem cá, quero te mostrar uma coisa!Come here, I want to show you something!towards the speaker → vir
• Já vou! Só um minuto.Coming! Just a minute.towards the listener → ir
• Meus primos vieram de Rio Branco e trouxeram castanha-do-pará.My cousins came from Rio Branco and brought Brazil nuts.vieram, trouxeram
• Vou levar um bolo pra festa da Iara.I'm going to take a cake to Iara's party.elsewhere → levar

Contrasts and traps

• "I'm coming" to someone who calls you is Já vou! or Tô indo!, because you go towards them. Tô vindo sounds wrong here.
• bring or take to a party? If the party is somewhere else, levar: Vou levar vinho pra festa. The host, speaking about her own house, says traz: Traz um amigo!
• vim / vi: vim = I came, vi = I saw. vieram / viram: they came / they saw.
• vimos is both "we come" (vir) and "we saw" (ver). "We came" is viemos.
• vem / vêm / veem: he comes / they come / they see.
• traz / trás: traz = brings; trás = behind (atrás).
• No preposition before an infinitive: veio visitar a gente, vem ver, not veio a visitar.

If you speak Spanish

The logic is exactly that of ir / venir and llevar / traer, so ¡ya voy! is Já vou! The forms are the trap: vine → vim, vino → veio, vinieron → vieram, traje → trouxe, traigo → trago. Traje in Portuguese is a noun, an outfit. And recoger a alguien is buscar alguém, while buscar las llaves is procurar as chaves.