Prepositions or conjunctions?

Some words which are prepositions also function as conjunctions. When we use a preposition that is followed by a clause, it is functioning as a conjunction; when we use a preposition that is followed by a noun phrase, it stays as a preposition. Among the most common are after, as, before, since, until:

After I’d met him last night, I texted his sister at once. (conjunction)
After the meeting last night, I texted his sister at once. (preposition)
We’ll just have to wait until they decide what to do. (conjunction)
Okay, we’ll wait here until six o’clock. (preposition)

since

As a conjunction since is sometimes ambiguous, because it can express a relationship of either time, or cause and effect:

➖They haven't stopped talking since they arrived (time)
➖The others just smiled since they were too polite to interrupt (cause)

The first use is more common than the second, and it coincides with temporal use of since as an adverb and preposition. Yet the second (causative) use hangs around as an alternative possibility in sentences such as:

➖The children have avoided going out since their father lost his job.

yet

The word YET functions sometimes as an adverb and has several meanings: in addition ("yet another cause of trouble" or "a simple yet noble woman"), even ("yet more expensive"), still ("he is yet a novice"), eventually ("they may yet win"), and so soon as now ("he's not here yet"). It also functions as a coordinating conjunction meaning something like "nevertheless" or "but." The word yet seems to carry an element of distinctiveness that but can seldom register.

but VS yet

Actually, (but,yet) are used as 'conjunction or adverb'
As an adverb,they are NOT interchangeable.They have completely different meanings.
Apart from "adverb', we can use (but,yet) interchangeably, they are similar when they are used to introduce a contrasting idea: (conjunction)
The room was small but comfortable.
The room was small yet comfortable.

Although they are similar in this use, they have slightly different usage and meanings .
"But" just means "but".
"Yet" is usually used when there's some kind of contrast or (surprise) involved.
"He's a doctor, but he does cartoon voices part time."
(Nothing strange here.)

"He's a doctor, yet he smokes." (It's strange, surprising and paradoxical that a medical person would smoke.)
"He walked in the door, but nobody saw him."
"He shot the man in front of 50 witnesses, yet nobody says they saw it.

discuss about❌❌❌

The verb discuss is never used with the preposition about. It is simply followed by a direct object:

✗ I would like to discuss about the advantages and disadvantages of students using credit cards.
✓ I would like to discuss the advantages and disadvantages of students using credit cards.

The longer I study English, the more I realize how little I know.

EVERYWHERE → ✔️

ANYWHERE → ✔️

But

Everyplace → informal

Anyplace → informal

Should of → ❌

Could of → ❌

Would of → ❌

Should have → ✔️

Should’ve → ✔️

Could have → ✔️

Could’ve → ✔️

Would have → ✔️

Would’ve → ✔️

Use “nor” after a “not” statement:

I DO NOT play the violin 🎻, NOR do I play the sax. 🎷

Ali CAN NOT swim 🏊, NOR CAN he surf. 🏄

1-It is not permitted to smoke in the office.[✔️]
2-You are not allowed to smoke in the office. [✔️]
3-It is not allowed to smoke in the office.[❌]

►The passive structure with ( it ) is only possible with 'permit'.