Words in a phrase

Im starting to learn japanese by myself and there's something I don't understand. I still don't read properly japanese letters but how do I know what's each word in a phrase?? For example this one:

さあ、あなたならどっちを選ぶ？

I know さあ is "come", but now that Im learning how do I recognize the words in the other part of the phrase (cause that's not a single word, isn't it? :? )

You have to learn a lot of vocabulary first. When you do, you will recognize "anata", "nara", and "dotchi" as separate words. When you can recognize the separate words, you will not need to put spaces between them. Until then, you need get a beginner's textbook, which puts the spaces between the hiragana words.

さあ is the interjection "come on, come now" not 'to come' the verb, if that's what you're referring to. The entire sentence reads あなた なら どっち を 選ぶ？
(If it were you, which would you choose?)