The word אבא means "Daddy". The word for father is אב, and the י at the end means "my". If you want to say "your father" etc. you start with אבי and then add the suffix ך --this is because אבי is also the construct form of אב . (Constructs may be in a later lesson, but I clicked on "strengthen skills" and I'm not sure what lesson this is.)
It is really fun too see how the semitic languages all do this in a slightly different way, like "imkha" in Hebrew, "emmak" in Arabic and "yimmokh" in Assyrian. All very concise and fine ways to insult your semitic friends. All you need for good insults in Hebrew is "imkha" and a couple animal names like "khamor", "kelev" and "gamal".
The problem is, words can't be neuter in Hebrew. So ילד means "child", but is male, so it means a boy. But there is also the word בן that means boy (it also means son, but that's besides this point). And it's like, if you say בן, you are being more specific. If you wanted to talk about a child generally, you would say ילד. If you wanted to talk about a girl you would say ילדה or בת. And ילדה can't describe a general child with an unspecified gender because life and language are unfair. :-(
The author Amos Oz once told about a story he wrote, with the opening sentence תחילה רגשו הכפרים. It was translated to English, he told, as "It began with the outbreak of rebelliousness in the villages". 3:10, though granted it's literature, and I'm not sure this English translation is as concise as it could and should have been.