The second tier of Fast Fingers requires you to cancel 25 normal attacks into specials.
A normal attack is performed by pressing any of the 6 attack buttons.
A special attack is a more powerful attack, usually performed by doing a motion on the stick+a button. For example, Ryu’s fireball, which is performed by inputting +. All inputs for special attacks can be viewed in your characters move list.
A cancel when you interrupt the animation of a normal move with a special attack. This is what allows normal moves to combo into special moves.
As an example, you can press with Ryu, and as soon as comes out, you can input + to cancel the animation into a fireball.