You can find a few other useful links in the corresponding tag info. Since you specifically asked about number of flags, this is explained in the answers to this question: On the recent changes to flagging and limits. There is not much to add, but for better accessibility, I will copy the answer here:
You start with 10 flags per day.
Based on your reputation and flagging history, you can end up with as many as 100 per day.
Currently, that means you get an extra flag per day for every 2000 reputation points or 10 net helpful flags (helpful-declined).
Briefly summarized - starting from 10 flags, you can get eventually get up to 100 available flags per day. The number of flags is increased based on the reputation and whether your flags are deemed helpful. I will also add that number of flags is always tied to a specific site. (For example, it is possible that you have 17 flags available on Mathematics, 12 on Mathematics Meta, but only 10 on Mathoverflow.)
Having many declined flags can lead to being banned from flagging. For more detailed information see the flag-ban tag-info on Meta Stack Exchange and the answer here: Allow recovery from flag hellban.