The ultimate aim of language learning is to be able to converse freely and fluently about everything and anything.
This isn't easy to achive, but one way to help is to learn a range of phrases and expressions which cover the different areas that you want to speak about or that you are interested in.
Learning phrases covering specific topics is useful for even advanced language learners. One point that is not mentioned (by language courses) is that even after you have become competent at communicating in Spanish, you still will not know the vocabulary needed to talk about everything. Just because I can talk about the weather doesn't mean I can discuss nuclear physics.
The links from this section of Simplest Spanish cover different conversational areas and topics from saying hello to asking about family.