If I block someone's number, does it still ring on their end when they call?

Yes on most networks and devices, when you call someone who has blocked you, the call rings briefly on your (the caller's) end before being redirected. You are not told you have been blocked.

On iPhone: caller hears one ring, then goes directly to voicemail. The blocked caller can still leave a voicemail, but it goes into a separate "Blocked Messages" folder the recipient never sees unless they choose to look. The recipient gets no notification of the call.

On Android: behaviour varies by manufacturer, but typically the call is immediately or quickly redirected to voicemail.

On some carriers: the call is silently rejected with no ring at all, or the caller hears a tone indicating the number is unavailable.

The blocked caller cannot tell with certainty whether they are blocked or whether the person simply has their phone off both experiences look similar.