klar
clear
Easy to understand, unambiguous, and without doubt.
Seine Anweisungen waren kurz und klar.
His instructions were short and clear.

clear
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clear
Easy to understand, unambiguous, and without doubt.
Seine Anweisungen waren kurz und klar.
His instructions were short and clear.

When 'klar' (clear) describes an abstract thing like an idea or a statement, it means 'understandable'. When it describes a physical substance like water or glass, it means 'transparent'.
Das war eine klare Anweisung.
That was a clear instruction.
The expression 'Alles klar!' is very versatile. It can be used as a question ('Did you understand everything?') or as an answer ('Yes, I understood.' / 'Yes, everything is all right.').
Wir treffen uns um 8 Uhr. Alles klar?
We're meeting at 8 o'clock. All clear?
In the meaning 'understandable', 'klar' (clear) is often used with nouns from the area of communication. Typical phrases are 'klare Worte' (clear words), 'eine klare Antwort' (a clear answer), or 'eine klare Struktur' (a clear structure).
Ich erwarte von dir eine klare Antwort: Ja oder Nein?
I expect a clear answer from you: yes or no?
As a standalone answer, 'Klar!' (Sure!) is a very common, colloquial way of saying 'yes, of course' or 'naturally'. It expresses casual agreement.
Kannst du mir kurz helfen? – Klar, kein Problem!
Can you help me for a moment? – Sure, no problem!
When 'klar' (clear) describes a mental state, it is often used in connection with 'Kopf' (head) or 'Gedanke' (thought). Fixed expressions include 'einen klaren Kopf bewahren' (to keep a clear head) and 'einen klaren Gedanken fassen' (to form a clear thought).
Auch in stressigen Situationen versucht er, einen klaren Kopf zu bewahren.
Even in stressful situations, he tries to keep a clear head.
The expression 'sich über etwas klar sein' (to be aware of something) is reflexive and uses the dative. The person who is aware is in the dative ('ich bin mir klar'), and the topic follows with 'über' + accusative.
Ich bin mir über die Risiken im Klaren.
I am aware of the risks.
natural / of course
'natürlich' and 'klar' can both mean 'yes, of course' as an affirmative answer. In this use, they are often very similar. 'klar' usually sounds a bit more casual and conversational, especially as a short answer. 'natürlich' sounds more neutral and also works well when you want to agree politely or clearly. Learners may confuse the words because both express agreement. But 'klar' can also mean 'clear' or 'easy to understand'; then it is not the same as 'natürlich'.

Klar, du kannst mein Fahrrad am Wochenende benutzen.
Sure, you can use my bike this weekend.
Natürlich helfe ich dir morgen bei der Vorbereitung.
Of course I'll help you with the preparations tomorrow.