New to Unity...Is there an easy way to block all interaction underneath a panel that I would have stationary at top of my game. There will be a pause button in that panel and some game info. Just don't want the mouse input or clicks to go through the panel and interacting with game below.
If you are trying to block interation on other UI elements (for example if this panel is a pop-up submenu or notification, which is overlayed on top of the actual menu, which is also made up of UI elements), then you can tick the "Raycast target" checkbox on the panel's Image component. This will prevent all clicks on the panel from going through the panel and interacting with UI components (such as buttons, checkboxes, input fields, sliders, etc.) underneath the panel.
If, however, you are trying to block interaction with game objects (and not ui elements), then there are also two cases I can think of:
If this panel is meant to stop interaction with the entire game (such as a "Game Options" panel, then you can do what Vadim Tatarnikov suggested and simply have a boolean which tracks whether or not the panel is open. Alternatively, since you mention pausing, you can also use the Time.timeScale static variable to determine whether the game is paused or not and use that to decide how to process clicks.
If this panel is however a screen overlay, where the player can interact with the panel, but also the game (for example a "Unit details" panel in a strategy game), then you can use what MrDiVolo suggested:
With this method, you however need to be very diligent in disabling transparent ui elements, setting the raycast target checkbox properly for all visible ui elements (meaning ticking for elements which should block clicks and unticking for overlays which should not block clicks)
I had a similar issue and I found this video to be very helpful, all credit to kiwasi.com. It's showing 3 possible solution approaches, from the simplest to most complex (and least to most recommended):