Arabs are a people whose place of ethnic origin is the Arabian Peninsula.
The language which they speak, and which has spread widely to other areas, is Arabic. “Arabic” is not generally used as an adjective except when referring to the language or in a few traditional phrases such as “gum arabic” and “arabic numerals.” Note that in these few phrases the word is not capitalized. Otherwise it is “Arab customs,” “Arab groups,” “Arab countries,” etc.
A group of Arab individuals is made of Arabs, not “Arabics” or “Arabians.” The noun “Arabian” by itself normally refers to Arabian horses. The other main use of the word is in referring to the collection of stories known as The Arabian Nights.
However, the phrase “Saudi Arabian” may be used in referring to citizens of the country of Saudi Arabia, and to aspects of the culture of that country. But it is important to remember that there are many Arabs in other lands, and that this phrase does not refer properly to them. Citizens of Saudi Arabia are often referred to instead as “Saudis,” although strictly speaking this term refers to members of the Saudi royal family and is usually journalistic shorthand for “Saudi Arabian government.”
It is also important not to treat the term “Arab” as interchangeable with “Muslim.” There are many Arabs who are not Muslims, and the majority of Muslims are not Arab. “Arab” refers to an ethnic identity, “Muslim” to a religious identity.
The standard pronunciation of “Arab” in American English is “AIR-rub.” Unless you are referring to the character in West Side Story called “A-rab” (with the second syllable rhyming with “cab”), you’ll sound better educated if you stick with the standard version.