This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
The exact historical development of 竌 is uncertain. It visually combines 立 and 几, but the original purpose and component relationship are unclear.
Since the meaning is uncertain, focus on the shape: a person standing (立) beside a table (几).
For ショ, imagine a show (ショー) where someone stands (立) on a table (几): show -> ショ.