This summary is not the rule. The rule text controls.
Here's a plain English summary:
If you're suing someone, you don't have to file separate lawsuits for each claim you have against them. You can combine all your claims into one petition, as long as it's just you (one plaintiff) suing just them (one defendant).
This works even if your claims are different types. You can mix legal claims with equitable claims, or claims that don't depend on each other, or even claims that contradict each other as backup options. The point is to let you bring everything you've got against that one person in a single case, instead of forcing you to go through the court system multiple times.
This saves time and money for everyone involved. It also keeps related disputes between the same two parties together, so a judge can look at the whole picture at once instead of piecing it together from separate cases.