Lieber jJohn,

wie geht es Dir?

And now it's getting complicated. You can capitalize in letters, mails, messages and so the informal direct adress pronouns like Dir, Du, Euch, Euer, and so on like you did here - but you can also leave them uncapitalized. But, if it's "Sie" (so the formal pronoun, not the 3rd person singular article) it always gets capitalized.

hHoffentlich ist alles gut, mir geht es zurzeit super.

New sentence, so you should capitalize the first letter. But a good sentence! "Super" might be a bit old-fashioned IMO, but it is still in use and correct.

Du weißt ja, ich habe mich für einen Computerkurs angemeldet ,d. Die Computerkurs Sschule ist 5 Minuten von meinem Haus entfernt ,und Studenten bezahlen 20 % weniger kKursgebuühren .

in the first part of the sentence, you need "mich" as a reflective pronoun so it's clear who entered the course. While it is not incorrect, I decided to split the sentence apart here - it just sounds nicer to me but that is a stylistic choice. "Computerkursschule" is written together and you don't need a comma before the "und". Kursgebühren is a substantive, so it's capitalized. Also, if you can't remember how to type the Ü, Ä, and Ö you can write ue, ae and oe as well (and replace them with your writing programm after). That writing is also usually used in crosswords as well!

Am Donnerstag haben wir angefangen d. Der Kurs findet jeweils montags und donnerstags von 19 Uhr bis 22 Uhr statt.

You can write a run-on sentence and connect them with a Komma between "angefangen" and "der", but I've chosen to split it up. Because of that, "der" is capitalized because it's a new sentence. You also need to add the "statt" because the verb in its entirety is "stattfinden" - and the "statt" moves to the back of the sentence after the time (and/or place, so "Der Kurs findet um 19 Uhr in der Schule statt"/"Der Kurs findet in der Schule um 19 Uhr statt").

Was hat mir sehr gefallen hat, ist, dass dier Computer neu sind neu undund wirklich gut funktionieren wirklich gut, auch unsere Lehrerin ist nicht nur interessant, sondern auch talentiert ,a. Außerdem sie macht sie einen tollen Unterricht.

The "hat" is needed because it's Perfekt, and up to there the whole sentence part acts as your subject and it's split apart from the "ist" by the comma. Then you begin a "dass" clause, which is a side clause depending on the main clause (or another side clause.). Which also means that the main verb moves to the back of the individual side clauses ("neu sind" and "gut funktionieren") because "dass" is a Subjunktion. "Auch", meanwhile, initiates a side clause with a Konjunktion which means that the sentence order is back to Subject-Verb-Object. And "Außerdem", if it's at the beginning of the sentence, also turns the sentence structure around, with the verb coming first. If you want to keep it in the SVO order, you need to insert it into the sentence after the verb, so "Sie macht außerdem einen tollen Unterricht."
As a general advice: If you are not sure about the syntax and grammar and Konjugations and whatnot of a sentence with subclause, keep it as simple as possible. As in, one main clause + one sub clause, not a main clause with a subclause and one subclause for the subclause. Or build it on an extra paper step by step, first inserting one subclause, then the other.

Ich habe mich für diesesn Kurs entscheieden, weil meine Computerkenntnisse für die neue Arbeit nicht ausreichend ist dsind(, weswegen sollte ich diesesn Kurs nehmen sollte).

Again, you need a "mich" here to specify that it was you who made the decision, and it's "entschieden" in the to make the Perfekt (you made the decision in the past and the effects continue on). Sub clauses always need a Komma, unless it's a subclause introduced by "und" or "oder". Computerkenntnisse is the plural (die Kenntnis - Die Kentnisse) so the verb is also in plural. The last part is technically not necessary IMO, because you already wrote the logical steps (not enough know-how --> take course) so it's just needlessly doubled basically.
For the sake of the grammar lesson: here you need "weswegen" not "deswegen". Weswegen introduces a "Weiterführender Nebensatz". Normal sub clauses refer to one part in particular of the sentence, "Weiterführende Nebensäte" refer to the meaning of the whole sentence. It also turns the sentence order around to SOV.

wWir können zusammen inach dern Kurs gehen.

It's "in den Kurs". It's a bit hard to explain but it's kinda like the Kurs is a room you go into if that makes sense?