Anion vs cation electron configurations

[Sophia Henry]

So here I see that when you write the electron configurations of ions you have to do it differently depending on whether you're doing it for a cation or anion. I see that for a cation you have to remove the outermost electron and for an anion you have to add electron until the next noble gas configuration is achieved. This sounds good on paper but I don't know what it means. How do you know what the outermost electron is for a cation and how do you know which specific part of the electron configuration that youre supposed to remove an electron from? And then again, not to sound dumb, but for anions.. How do you know which part of the configuration to add 1 electron to if its a -1 anion? Why do you add an electron to one and take away an electron for the other?

[jedricgonzales2I]

When removing the electrons while writing the configuration of the cation, the outermost electrons refer to the electrons in the valence shell. The valence shell can contain s, p, and d subshells. You would take from the s subshell first, then the p subshell, and then the d subshell. This is the same thing in reverse for anions; you would add electrons to the lowest energy subshells.