I think it's a question we all have done once in ours lives when we were about to learn a new language.. And for your case, i think its Korean, right? Well, personally I don't know nothing about it, but I can say that for me it's kinda easier to learn first vocabulary, nevertheless that doesn't mean I will wait a long period to begin to learn the grammar. It's a process that goes by the hand, nor the grammar can work without vocabulary, neither knowing a lot of words will be useful if you don't know the structure where to put them in. But, i'm pretty sure that having a wider vocabulary will help you to make sentences more complex, and you won't have problems with the fact of expressing yourself

I think you should learn basic grammar and top 50-100 most popular and useful words at first. It can help you to start dialogs, chats and so on almost immediately after it.