There are different ways you could provide a random number.
1) App Inventor has a random number block in the Math section
2) App Inventor has a pick a random item list block om the List section
3) perhaps
will give you ideas?
Do you need an actual spinning wheel? If you need a graphic, the problem becomes a little more complicated. You will probably need to use the Canvas ... consider reading
A very good way to learn App Inventor is to read the free Inventor's Manual here in the AI2 free online eBook
http://www.appinventor.org/book2 ... the links are at the bottom of the Web page. The book 'teaches' users how to program with AI2 blocks.
What have you tried so far? This is your school assignment. You can see what others have done for similar topics by searching the gallery for random

and download and review the provided aia files.
Merry Christmas, Wesołych Świąt, Feliz Navidad, God Jul, Joyeux Noel, Καλά Χριστούγεννα, Happy Christmas, Veseloho Rizdva, Prettige Kerstdagen, Frohe Weihnachten!, 성탄 축하 , Buon Natale, 聖誕快樂 , 圣诞快乐, Sretan Božić, C рождеством!, عيد ميلاد مجيد,
-- Steve