One person stands in front of a large group of players. Every player is holding a different part, and none of them can hear the whole thing. The person in front decides who comes in, when, and how loudly. From where the audience sits, all those separate lines arrive as one sound. Every use of orchestrate is some version of that: many different parts, one person deciding how they fit, and a result that feels like a single thing.
From the word’s history
The supplied source gives orchestrate as orchestra plus the verb-forming ending -ate, and compares French orchestrer. The conductor picture is therefore inside the word itself, not added afterwards.
資料裡寫的是 orchestra（管弦樂團）加上動詞字尾 -ate，並且對照法文 orchestrer。所以「樂團」這個畫面本來就在字裡面，不是後來才貼上去的。
Wiktionary etymology supplied in evidence packet (kaikki:3f6f69a190036ae4:825078280): orchestra + -ate; compare French orchestrer.
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