Ohaio

Watashiwa namaie Kiria desu. Watashi wa nihongo o benkyo shi  hajimeta 

ohayou

watashi no namae wa kiria desu .watashi wa nihongo o benkyoushite hajimeta .

おはよう

私の名まえはキリアです。私は日本語を勉強して始めた

Ohaio --> Ohayou

(*the formal way to say it is "Ohayou gozaimasu", and in this note it's better to use the formal form to introduce yourself for the first time.)

Watashi nowa namaie wa Kiria desu. (or Watashi wa Kiria desu.)

Watashi wa nihongo wo benkyou shihajimemashita.

(*"benkyou shihajimeta" is the casual form and "benkyou shihajimemashita" is the formal one.) 

Good job! If you already know the Japanese characters, please write with them. If you don't know them, I'd like to recommend you to remember them first, hiragana and katakana. Good luck!