@sonVishal: You didn't miss anything -- the debugger is still somewhat experimental and we don't have any docs for using it in Juno yet.
@zhangliye: We do have a debugger GUI, the breakpoints you can set with it just aren't working yet.
If you are on Julia 0.5 and have the newest version of Juno (Atom as well as Julia packges), you can do stuff like
Juno.@step gcd(12, 4)
either in the console or in the editor, which will bring up the debug UI and allow you to step through that function. When you do that, it's handy to also open the Workspace Pane (under
Julia > Open Workspace), which will show you the values of all variables inside the function you are in.
Regarding breakpoints: If you have say a file
test.jl, which contains
y = x
y = sin(y+x)
you can e.g. call
Juno.breakpoint("test.jl", 3) in the console, followed by reevaluating the function and then calling it. That should bring up our debugger UI as well on line 3 in that file.