In the top right corner of any Slate page, click Sign In.
If you created your account using your Facebook, Yahoo, Google, or Twitter account, make sure to click the appropriate button to log in.
Once signed in, you'll have access to unlimited articles and all of your podcasts will automatically play the ad-free extended versions in place of the regular ones here: https://slate.com/podcasts. You can find details about your Plus membership on your Slate Plus welcome page.
Signed in but not recognized as a Plus member? Check here for more info.
To access Slate Plus benefits inside Slate's iOS app, follow these instructions.