What is the different between "Speak" and "Talk"

I don't know when I use "Speak" and "talk"

is there a big problem if I make an error to choose one of them instead of other?

What is the purpose in life?

Does life have meaning?

if we looking and thinking about creation of the earth we will know which this earth has a creator (God),and created us for worshiping it and doing a favor each other, but our racism and  bad politician changed our life from happiness to depression.

what is the most common App for Conversation? I heard many app or social communication for conversation but I don't know what is the best one.

what about Racism?

White's skin does not consent of Black's skin or Different in religions don't consent each other ,Why we don't live as a human and don't bother anyone?! 

Did you agree with this sentence "You don't have to complete the studying to be a famous man/women? many people saying the studying is not the way to be success in your life such as the founders of huge electronic company all of them didn't complete their studying, but I think their studying lead to think more and grew their mind till get the desireable results.

What are the Secrets for learning languages? I saw many ways or methods for learning language, but I don't know what are the best way for learning.

Give me some tips about IELTS If possible discuss about Speaking part I will be thankful.

Self Confidence Don't wait fro anyone to improve or change your life,but try and Strive by yourself to Change your life to better.

What is your opinion about Hypocrite people? "Hypocrite" mean the people having two faces. So Just I want to see your opinion and you can Define that