MSD (Mina Standardized Difficulty) is calculated using a process that starts with a few key inputs: a list of NoteInfo entries (each describing which notes appear on a given row and the time of that row), the percent (score goal) you’re calculating for, and the music rate (which adjusts the timing of the notes based on song speed). The chart is divided into half-second intervals spanning from the first note to the last. Each of these intervals gets its own difficulty value for every skillset (jumpstream, handstream, technical, etc.) and for each hand.
Each skillset has a different algorithm to determine difficulty. Some rely on basic note density, like notes per second (roughly 1.5 times the number of notes), while others like technical, jackspeed, and stamina use more complex logic. For every interval, the system calculates the likelihood that a theoretical player would lose Wife points based on the difficulty of that section and how many notes it contains. These point loss estimates are then fed into an iterative calculation process, similar to the one used for determining player ratings, which ultimately figures out how hard the entire chart is for each skillset, excluding stamina.
Stamina is handled differently. Instead of being based on per-interval judgments, it’s derived from how much a skillset rating changes between the first and second passes of the difficulty calculation, effectively measuring the strain of sustained difficulty across the whole chart. Once all skillset ratings are established, the overall MSD for the chart is typically the highest single skillset rating, or slightly higher if multiple skillsets are similarly demanding.
In any case you should think of MSD as a rough general gauge of difficulty that doesn’t take much technical minutiae into account. Seeing as you recently just started playing, these values will not mean as much now as they will later.