To subscribe to a reading plan on Bible Gateway, you will need to have a free Bible Gateway account. If you don't already have an account, you can create one by following the directions here. Once you have a Bible Gateway account, go to the Reading Plans page at https://www.biblegateway.com/reading-plans/ :
The Reading Plans page lists out the different Bible reading plans available to you, like this:
Each reading plan approaches the Bible in a different way--some reading plans walk through Scripture from beginning to end in the course of a year, while others change the reading order or duration. Once you've identified the reading plan you'd like to try, click Subscribe below its name to pull up a subscription calendar:
By default, the reading plan is set to begin on the current day. You can choose a different start date by clicking on a different date in the calendar. You can also choose to receive an email reminder when new readings are ready by checking the Yes, please send... checkbox. Once you've chosen a start date, pressing the Start This Devotional... button will subscribe you to the reading plan.
Now that you're subscribed to the reading plan, you can access it at any time by visiting the Reading Plans page. Reading plans to which you are subscribed are listed near the top of the page; click Read Plan to read the current reading, or Manage Plan to pause, restart, unsubscribe, or make other adjustments to your subscription. If you opted to receive email reminders when new readings are ready, you'll receive a reminder on the day that any new reading becomes available; the email reminder contains a link to the new reading.
Remember, you must be logged into your Bible Gateway account to access your subscribed reading plans.