They are almost the same, have a look on this short lesson to know what is the difference, a simple lesson with some helpful examples :) http://speakspeak.com/resources/english-grammar-rules/various-grammar-rules/speak-talk-differences

speak and talk can be used in the same sentence in a lot of situations, for example, I will speak to John I will talk to John But there are also situations where we can only use one. These are called collocations where a native speaker thinks the incorrect use sounds wrong. I am learning to speak English - sounds correct. I am learning to talk English - does not sound correct. Let's speak things over - does not sound correct. Let's talk things over - sounds correct.

Olá compatriota, talvez este vídeo possa te ajudar a diferenciar Say, Tell, Speak & Talk: https://www.youtube.com/watch?v=LSD-_iNl8m4