Sharing with Only Some People
With Free and Pro accounts you can only make a dashboard public or private. If it's public, everyone in the world can view it but only you can edit it. If it's private, only you can view it.
If you want to share a dashboard with only specific people, though, you're going to need a business account. The Business dashboard permissions page has detailed information and screenshots.
Sharing with Everyone
Sharing your dashboard with the world is easy. There's a share button on your dashboard's overview screen.
If your dashboard is public, you can click the share button and it will bring up the share sheet.
You can also just copy the dashboard's URL in your browser and share it with people any other way you want.
If your dashboard is private, however, the share button will be disabled and any other people who visit that dashboard's URL won't be able to see it. To make your dashboard public, just click the gear icon.
Then, on the permissions tab, you'll see a privacy switch.
Give it a click and it will switch to public.