Bonjour à Ttous, ¶
je suis totalement nouveau ici, je suis en train d’'apprendres le français par moi-même via YouTube undet Facebook.

No need to pluralize "tous"
"être en train de" is really used for things you're doing at the very moment you're talking/writing. You'll most likely keep on learning French after finishing this text, so the présent simple would be far better
Alternative => j'apprends le français en autodidacte

Tout d’abord, je voudrais vous me présenter un peu à vous.

"me vous" would technically be right, but it's never used

Je suis Vvietnamien, à l’âge de 20j'ai 20 ans, je suis sorti du lycée l’an dernier, et maintenant je ne sais pas quel chemin que je vais choisir dans(à l’avenir).

Ethnicity adjectives are capitalized only when they're used as nouns
This would require a complement ("à l'âge de 20 ans"), but this formal structure is used as an adverbial complement. "I'm 20" simply is "j'ai 20 ans"
You're not repeating anything at the end of the sentence, "quel chemin je vais choisir" is the object of "savoir"
We say "À l'avenir" but this wouldn't be necessary here, since you already have a future structure ("vais choisir")

La vie est très dure pour moi.

Feminine agreement with "la vie"

Il est difficile àde trouver un boulot, parce que beaucoup de gens élevés avec leur diplômeés n’ont pas de travail approprié.

Simple verb complements require "à", ex "c'est dur À dire" = "it's hard to say". However, when an adjective starts a whole clause, "de" is used
"élevé" means "raised". You can be raised with siblings ("élevés avec des frères et soeurs"), "raised with love" ("élevé avec amour"), but "raised with a diploma" feels highly strange, as if you had a diploma from your very infancy on
un diplômé = a graduate

Je sais pas si je vais continuer à étudier à l’université ou bien je m’occupe d’un faire le travail de mes parents qui [vendent des choses aux enfants à la maison. ?]

This one isn't a true conditional "si", it's a "si" presenting alternatives. So if the actions afterwards are meant to happen in the future, the verbs can and must have future forms
"s'occuper de" would mean "to take care" (to ensure something's done)
The end is a bit vague to any reader: they sell things to kids? Which kids and which things?

Je me le trouve ennuyéant et mal au salairepayé.

ennuyANT = causing boredom (present participle) ; ennuyé = feeling boredom (past participle)
"mal au salaire" doesn't exist

Si j’étudie à l’université, mon futur serait peut-être brillant, qui sait ?

You have two options:
Likely hypothesis, if A happens, B will follow => present in the "si" clause, future in the main one
Unlikely hypothesis => imparfait in the "si" clause, conditional mood in the main one

Both are right here, the difference depends on the likelihood degree you want to give the sentence

Merci pour/de votres corrections !

I corrected several sentences, so the plural would be better