I'm not sure if you have read Steinbeck's Of Mice and Men, but a clear allusion is the title of his novel which alludes to a poem by Robert Burns called "To a Mouse." This is a pretty simple allusion to describe if you have read Of Mice and Men.
The Great Gatsby is full of historical allusions. One example is when Nick meets Gatsby's shady business "partner" Wolfsheim and discovers that Wolfsheim helped throw the 1919 World Series--a blight in American baseball history that really happened.
If you can use songs, you will find numerous examples of allusions in them. For example, a song by James Blunt which appears on his first album contains an allusion to the literary character Dorian Gray. The song is entitled "Tears and Rain," and in it Blunt expresses his wish to hide his "true shape, like Dorian Gray" (line 9) so that he can forget his poor choices in life. In literature, Dorian Gray is the title character from Oscar Wilde's Picture of Dorian Gray and makes a deal with the devil to be able to live his life however he wants without reaping the physical or spiritual consequences associated with a life of debauchery. Instead of his aging, a portrait of him in the attic begins to show all of the horrible things Dorian has done.
Many modern rap songs also contain allusions or references; so just choose something that you are familiar with and see if you can find the allusions. I also posted some links below that might help you.