Three consonants carry one forceful idea: to press a claim. In everyday speech it is a demand; in the courtroom it becomes a lawsuit. The same root names the one who demands (the prosecutor) and the act of demanding (the claim). Notice how the legal sense and the ordinary sense are not two words but one root seen in two settings. Every word here is verified against pealim, niqqud included.
The same root runs through the verb system. Each binyan is a voice: it bends the one idea into active, passive, causative or reciprocal. Tap to hear.
Only two binyanim are lexicalized here: the active pa'al (to demand) and its passive partner nif'al (to be sued). The pi'el, hif'il and hitpa'el slots stay empty for this root. That is normal: not every root fills all seven binyanim.
Same root letters, different noun moulds (mishkalim). The mould tells you the function: who does it, the act of doing it, or the thing produced.
Strip the prefixes, suffixes and vowels. Three consonants remain, and the meaning lives there.