New to Swahili
As the title says, I am new to Swahili. What is the difference between "njema" and "mwema"?
You will find Kiswahili to be challenging for the reason of there being so-called noun classes. In general, the word stem in Kiswahili is not located on the left-hand side. Therefore, the beginning [!] of a word will change with agreement.
Let me give you an example for agreement differences based on English:
The plural morpheme attaches at the end (i.e., right-hand side). Now to Kiswahili:
Here the beginning of the word changes. The same holds, and here we finally get to agreement, for adjectives or verbs. Those have to follow the paradigms of the nouns:
The boy reads mvulana anasoma.
The boys read wavulana wanasoma.
It is best to learn the noun classes along with vocabulary (even though they are thematically related most of the time, there are exceptions).
Take a look at this link for an overview: https://www2.ku.edu/~kiswahili/pdfs/Lesson_09.pdf
Work through it and you will find yourself an answer to your specific question (I shall not be spoiling too much here c-; )
The rest of the language is pretty easy though. Heads up!