Voice settings and what to do if nobody can hear you

Open User Settings → Voice & Video Settings.

Voice

Pick a microphone and speakers / headset. There is a mic test.
Transmit mode: voice activity or Push to Talk. PTT has no default key — assign one under Keyboard Shortcuts. Mouse buttons are allowed.
Global PTT (when Astral is unfocused) works only in the desktop app. macOS needs Input Monitoring.
Cue sounds: join / leave / move, mute, camera, screen share. Custom sounds are a Plutonium perk (file up to 2 MB).

Default camera, preview, and video background. Custom backgrounds: 1 free, 15 with Plutonium.

Check that you are not muted or deafened in the user panel.
In voice settings, confirm the right device — virtual cables and Bluetooth headsets are frequent culprits.
Allow the microphone in the browser / Windows / Android. Rejoin the channel after changing the permission.
In PTT mode, hold the assigned key. If none is set, assign one.
Quit other apps that capture the mic exclusively.
Try another device or the web client to see whether the problem is hardware or the app.

Still stuck? File a report: Reporting a bug to Astral.