Je dois apprendre Fle français pour l’école.

Adjectives and language names are always written in lowercase.

Je dois eécrire une lettre ce semestre. ¶

Je ne suis pas bieon. ¶

"Je ne suis pas bien" = I am feeling kinda sick, in colloquial French
"je ne suis pas bon" = I'm not good (at something)

Je vais essayer d'écrire souvent ici. ¶

Je dois apprendre Fle français pour l’école.

Don't forget the article: we say "apprendre LE français"! ;)
Also, in French we don't use capital letters at the beginning of language names. (Sometimes we need them for nationalities but it's a bit complicated, I'm sure you can look up the rules on the Internet!)

Je dois eécrire une lettre ce semestre. ¶

Just the acute accent on "écrire"

Je ne suais pas bien. comment faire./Je trouve cela difficile.¶

In this context, "Je ne suis pas bien" doesn't sound very natural in French (or at least not very formal).
You could use one of the sentences I suggested to express the idea that writing a letter in French is difficult to you.

Je vais essayer d'écrire souvent ici. ¶

"try TO do something" is "essayer DE faire quelque chose".
(and "de" becomes d with an apostrophe before a vowel-initial word like "écrire").

Merci, au revoir !

Ponctuation rules in French are a slightly different but don't worry too much, even French people don't usually know all of them.
In this case you need a space before the ! exclamation mark.
This rule also applies to most two-part symbols, such as ; : and ?