Question: How do I use the interactive debugger?

Sorry if this is stupid but How do I use the interactive debugger?   the button is greyed out for me and 

stopat(EAdd(x^3+2x+1,x, 13, 1, 2, 1, 2), 1);

Error, missing operator or `;`


stopat(EAdd, 1);


debug button is still greyed out IDK what to do now

p.s. is there a way to set breakpoints in your code by clicking like in other programming?

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