Bescheid sagen/geben
to let someone know
To inform someone about something or send them a message.
Kannst du mir bitte Bescheid geben, sobald du zu Hause bist?
Could you please let me know as soon as you get home?

notice / information
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to let someone know
To inform someone about something or send them a message.
Kannst du mir bitte Bescheid geben, sobald du zu Hause bist?
Could you please let me know as soon as you get home?

The most important difference: In the expressions 'Bescheid geben' (to let someone know) or 'Bescheid wissen' (to be informed), the word is used without an article. When it means an official document, it is a normal noun with an article ('der Bescheid', the notice).
Ich weiß Bescheid, danke!
I'm informed, thanks!
The expression 'Bescheid geben' or 'Bescheid sagen' (to let someone know) always needs a person in the dative who receives the information. The structure is: jemandem (dative) Bescheid geben.
Gib mir bitte Bescheid, wenn du fertig bist.
Please let me know when you're finished.
If you want to say what you are informed about, you use the preposition 'über' with the accusative. The structure is: über etwas (accusative) Bescheid wissen.
Weißt du über die neuen Regeln Bescheid?
Are you informed about the new rules?
As an official document, 'der Bescheid' (the notice) is often combined with verbs that describe a reaction. Typical examples are: 'einen Bescheid erhalten' (to receive a notice), 'einen Bescheid prüfen' (to review a notice), or 'Einspruch gegen einen Bescheid einlegen' (to file an objection against a notice).
Sie müssen innerhalb von vier Wochen Einspruch gegen den Bescheid einlegen.
You must file an objection against the notice within four weeks.
In the meaning of 'offizielles Dokument' (official document), 'der Bescheid' belongs to administrative language (official German). You find the word in letters from offices, authorities, or insurance companies.
Laut Bescheid müssen wir eine Gebühr nachzahlen.
According to the notice, we have to pay an additional fee.
to know
'wissen' and 'Bescheid' are connected when it comes to information. 'wissen' is a verb and generally means that you have a piece of information. 'Bescheid' often appears in fixed expressions such as 'Bescheid wissen' (to be informed / to know what's going on), 'Bescheid sagen' (to let someone know), or 'Bescheid geben' (to let someone know). So you do not simply say 'Ich Bescheid', but 'Ich weiß Bescheid' (I know / I’m informed). In addition, 'der Bescheid' can also be an official notice from an authority. Learners easily confuse the words because 'Bescheid wissen' means almost the same as 'wissen', but it is used differently in grammar.

Sagt mir bitte Bescheid, wenn ihr nach dem Essen losfahrt.
Please let me know when you leave after dinner.
Morgen weiß die Nachbarin, ob der Handwerker kommt.
Tomorrow the neighbor will know whether the repairman is coming.