CanadianCrafter

I have a quick question. ごめんなさい is sorry right? but when I used a hiragana chart I noticed that there is no "go" but ko which is こ. I notice that a lot of the time there are markings like quotation markings at the side. What is this called and are there more symbols like it? I'm assuming that it alters the sound and perhaps meaning of the 48 hiragana characters. Would this also mean that the 48 are base characters with these symbols added onto them? Thanks.

OVA Stranger in 10 Years ending (kinda would want that).