I'll show you some examples.
First of all, about か（ka）. For example, "Anata no namae/onamae wa nandesu ka.(What's your name?/ Can I have your name?)." "Onamae" is more formal as a question. But you can't say " Watashi no onamae wa Caitlyn.". ” Kare wa sensei desu ka.(Is he a teacher?)" "Ima nanji desu ka.(What time is it?)". "Anata wa doubutsu ga suki desu ka.(Do you like fruits?)".
Secondly, about "は(wa) ". Ex. You know, we read it as "ha" with the only one letter. But we read it as "ha" after a subject. "Watashi no namae wa Hanako desu./ Watashi wa Hanako desu.(My name is Hanako./ Watashi wa Hanako desu.)." "Iie, kare wa sensei ja/dewa arimasen.". "Dewa" is more formal. "Ima wa kuji gojyuppun desu.(It's nine fifty now.)". "Hai, watashi wa doubutsu ga daisuki desu.(I love animals.)".
At last, abuot "が(ga)". We use "が" when we'd like to emphasize something. Ex. "Watashi ga Hanako Tanaka desu.(I'm Hanako Tanaka.)" I'll say with "が" if there're some people are named "Hanako". "Kare ga anata no isha desu."(He's your doctor). I'll introduce you your doctor if there're some doctors there. "Watashi wa tokuni inu ga suku desu.(Especially I like dogs.)" I hope my explanation help you ^^