Question

what is the difference between muslims and arabs

Answer 1

Arabs are (mostly) Muslims, who speak Arabic.

Muslims worship the prophet Mohammed.

Answer 2

For a better definition of Muslim, see
http://en.wikipedia.org/wiki/Muslim

Answer 3

Traditionally, one was considerted a Muslim if you publically pronounced this:
Ash-hadu an laa ilaha illa-lah Wa ash-hadu anna Muhammadan rasulullah

"I bear witness there is no deity worthy of worship except Allah and I bear witness, Muhammad is His final messenger".
The problem with that it allows all sorts of folks to be good muslims: murderers, terrorists, thiefs, airplane bombers, and so forth.
Most Muslims agree that to be muslim, one has to say the above.
However, a few years ago, some muslims concerned with ethics, attempted to redefin what a muslim Is.

It said you had to be active in one of the major schools of thought on Islam:
1. Sunni Hanafi
2. Sunni Hanbali
3. Sunni Maliki
4. Sunni Shafi'i
5. Shia Ja`fari
6. Shia Zaidiyyah
7. Ibadi
8. Zahiri
All the other (sects) were "prohibited"
http://en.wikipedia.org/wiki/Amman_Message
Personally, I am not certain this edict will stick.
Time will tell.