first-come, first-serve basis

[Liqichao]

hi everyone,

how can I understand below words?
centra space here is sort of web meeting tool.

Centra space is on a first-come, first-serve basis

thank you very much

[Mister Micawber]

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The first people who make contact are the first people who may participate.
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Native English teacher at Mister Micawber's