How do you create splits for a specific game and once you are done, you download them? For example these are what I want for super mario galaxy: any% mario and luigi, 120 for mario and luigi, and 242. For galaxy 2 I would want 242 stars, and a Super mario galaxy series speedrun
Download Livesplit (most commonly used program) or WSplit (my personal choice). If you have a Mac, your only option is Llanfair.
Once you have it downloaded, you can run it and customize it's look and feel as you choose by exploring all of the settings an options (there are way too many to list here, but Livesplit is by far the most customizable). Once you do that, you simply add splits by right clicking on the program and choosing the Edit Splits/New Splits option. Then you put in whatever splits you want.
After that you can do save/save as to save the split file somewhere so you can always re-open those splits.
and if you're using a mac, the best program is Llanfair. (Livesplit only works with Windows)
https://www.reddit.com/r/speedrun/comments/5yj6o3/livesplit_mac/
I kinda want to raise awareness for Livesplit one; Browser splitter. Works with every OS :). The only downfall is that there are no global hotkeys
Since SMG is a pretty large game, I'm assuming they already have pre-made splits that you can download by going to the "Resources" tab on the game, so you don't have to make the splits yourself