We call the blue cards with helpful information on them, "Tip cards." These will automatically open up when you first encounter a new page or feature. You can open them anytime by tapping on the blue tab with the lightbulb on it.
To stop the Tip card from popping up again, tap, hold, and drag it down to the box icon that appears at bottom of the screen.
To bring Tip cards back after dismissing them, open “Help & Info” from the left side panel (accessible via the = menu or swiping left to right) and tap “Reset Tips.”