Can someone tell me what's the difference between Algebra 1,2,and 3?
What do you mean by algebra?
The algebra of high school (elementary algebra) or algebra of math majors (The study of various structures including groups, rings, and fields)?
That terminology is for the Algebra of Arithmetic in high schools. Look at the table of contents and topics shown of these books: Algebra 1 corresponds to Elementary or Introductory Algebra; Algebra 2 corresponds to Intermediate Algebra; Algebra 3 is questionable because something like this might be a combination course which mixes slightly more advanced Intermediate Algebra, Trigonometry, and maybe a few other topics, and the course might be called Mathematical Analysis at the high school.
In college, the level of the course of Algebra of Arithmetic which comes after Intermediate Algebra will be titled, "College Algebra" (although science & engineering students usually first study Trigonometry, and then enroll in "College Algebra And Trigonometry", often called "Pre-Calculus").
However, you should be aware that there is no law requiring every secondary school in every country to teach exactly the same courses! What is called "Algebra I" in one school may differ widely from what is called "Algebra I" in another.
Separate names with a comma.