Each Finger Has a Finger Number Piano
The short answer is it matters a lot when you first start learning. The reason that fingering is so important is that when you are learning a piano solo, five finger pattern or even a simple chord, your brain is memorizing not only the piano key note names but also the finger you are using to play each note.
Therefore, it is important to use the same fingering assignments over and over again as you practice the same passage or finger exercise pattern.
For example, when you are learning the simple Right Hand CDE piano piece, you are using your right hand first, second and third fingers over and over again to play C, D and E. Though it may seem as simple as can be, it would become more difficult if you were to use a different fingering pattern each time you played it.
Beginner Piano Lessons
Follow the finger numbering guidelines below. You will quickly learn the finger numbers both mentally and physically (i.e. your brain and fingers will coordinate an exclusive pathway for this skill set).
5 4 3 2 1 1 2 3 4 5
LEFT HAND RIGHT HAND
THE THUMB OF EACH HAND IS FINGER #1
THE INDEX FINGER OF EACH HAND IS FINGER #2
THE MIDDLE FINGER OF EACH HAND IS FINGER #3
THE RING FINGER OF EACH HAND IS FINGER #4
THE PINKY FINGER OF EACH HAND IS FINGER #5