Introduction

Konnichiwa! Hajimemashite.

Watashi wa Mōgan desu. Nihongo wo benkyo shite imasu. Amerikajin desu. Jugo-sai desu.
Watashi wa byōnin desu. Yoku natte imasu.

Sore dakeda.

Matane!

Hi. I've studied Japanese, so I know the basics.
the text is good, but did not understand the part of "Watashi wa byōnin desu"
if you mean that this patient better to use "watashi ga byounin''

"Wa" is used to mark something that has already been introduced into the conversation, or is familiar with both a speaker and a listener. (proper nouns, genetic names etc.) "Ga" is used when a situation or happening is just noticed or newly introduced.