Fighting games and their communities use several different types of notation. Some of this is purely personal / community preference, some is due to one system of notation not always working for all games.
2D fighters tend to have (more) consistent notation between them, with 3D fighters often differing from 2D fighters.
For JoJos, you are likely to see a few different kinds of notation.
For all notations, the directions given always assume you are on the 1P side, facing right. Typically (360s can be done either clockwise or counterclockwise) these will need to be reversed when your opponent is on your left.
 ??term?? Notation
 Whatsitcalled notation is used for several games and quite common in street fighter communities.
 Pros: Common in SF communities (important due to sheer popularity), more intuitive to english speakers at first glance than numpad notation.
 Cons: Englishcentric. Offers many overlapping options.
 Example: Your normal quartercircleforward+button 'fireball' motion with medium attack is: d,df,f+B, and dashing low C (such as Abdul's excellent sweep) would be f,f,df+C. However, this notation is laden with shorthand. Quartercircle motions are commonly referred to as QCF or QCB, Half circles are HCB/HCF, and so on.
A more full list of shorthand and other information is available at Sonic Hurricane's SF Notation Manual


 Numpad Notation
 Based on the numpad of a (fullsized) keyboard, numpad notation has a bit of a learning curve but is quite strong.
 Pros: Very precise, internationallyfriendly because it doesn't rely on english terms. Dominant Japanese notation (AFAIK).
 Cons: Scary to new players, takes some time to become intuitive.
 Example: Your normal quartercircleforward+button 'fireball' motion with medium attack is: 236B, and dashing low C (such as Abdul's excellent sweep) would be 6,6,3C


 Some other sites' usage and explanations of fighting game notation
 Dustloop  Guilty Gear
 Sonic Hurricane  Street Fighter