What is the point of those breakpoints?
Breakpoints are for debugging a project and are set by the developer. A breakpoint can be placed at any line of code and whenever that line is executed, the engine will halt the game and give you the chance to inspect e.g. the value of certain variables to determine when things go wrong and why. You probably set one accidentally, by left-clicking the area on the left of the line-numbers. Existing breakpoints are indicated with a tiny red square and can be removed again by clicking on it.
why does it show me errors for each signal I connect
Check the documentation. A call to
connect() is not returning nothing (
void) but an
Error instead. Which is an enum that tells if you everything works according to plan (then its value is 0) or not (then it's something else). What you get is a warning (not an error!) about the fact that you are not checking that error variable.
The technically correct-way of doing it would be:
var error_code = connect("dummy", self, "_on_dummy")
# or do something else about the error
As it's only a warning you can also disable it under Project > Project Settings... > Debug > Gdscript > Return Value Discarded, but I wouldn't recommend that.