Things to know about mania:
1: Autoconverts have terrible patterns. If you're serious about this game mode, avoid them unless you really just want to play for the music.
2: When you begin playing, your rank will rise quickly, when you fill your Top Scores list (as visible on your profile) it will slow down, because only scores in your top scores list will count towards your PP (which is what determines your rank).
3: Everyone learns at a different pace. Don't try to compare your learning against someone else and feel bad if they're learning faster than you.
4: Skill walls happen, keep playing and eventually you will beat them, but sometimes it can take a while.
5: Osu!Mania and other Vertical Scrolling Rhythm Games reward dedication. In standard, even at low skill levels it's possible to watch a player and notice that maybe their aim is causing them problems, but they can hot the keys fast enough. Because timing and aim are two separate things, you can practice one without the other in standard. This is not the case in mania, meaning there's no real way to train separate skills at low levels.
6: You will get better, even if t feels like you're not.
7: Go read
t/146615 and actually read the first few pages.
8: Have fun, and don't worry about ranking or PP. If you legitimately want to get good, the most important thing is to play songs out of your comfort zone in the beginning. When you start out, it's easy to panic and get overwhelmed by maps that feel too hard. Don't quit out when this happens, try your hardest to hit everything you see. Doing this will help you improve much more than focusing on improving an an A to an S, or a low S to a much higher S.