The core gesture is closing something shut. From it the family fans out in two directions. One is physical: a closure or curfew, a lock, the state of being closed, even the frame that closes a picture in. The other is human and harsh: when the hif'il closes a person in, it means handing them over, extraditing them. The same letters that lock a door also lock a person up. Watch how a closed border (סֶגֶר) and a picture frame (מִסְגֶּרֶת) are the same idea, an edge that shuts something in. 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.
Notice the semantic jump in the hif'il: literally "to cause to be shut in", it shifted to handing a person over to the authorities. The passive partners (nif'al, huf'al) are not the everyday vehicles here; the adjective סָגוּר already covers "is closed", and the noun moulds below carry the rest of the load.
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.