こんにちは

こんにちは、　ぼくはコーリーです。　ぼくはにほんごをべんきょうします。

According to my classes:

Your direct object "にほんご" must be indicated with を.

To say "hello", it must be used "は", pronounced as WA like it was a particle (In the past, it was "こん"=this "にち"=day "は"=as you say, the particle, and then maybe things like "is good", so "today is good", "how are you today?"...).

こんにちわ

こんにちわ　ぼくはコーリーです。　ぼくはにほんごをべんきょうします。