My house's door open outwards and overnight the snow has accumulated outside (to half the door height) and prevented the door from being opened.
What to do in this situation if we want to open the door and go outside?
Go out a door that's not blocked and walk to the blocked one to clear the snow.
If all your doors are blocked go out a window and do the same.
If it's a screen door, remove the screen and reach through the opening to move the snow. You can use a broom or even a pot or baking pan if your don't have a shovel within reach.
In most cases, snow is not a solid substance. It is powder so it has a bit of movement. What you have to do it push the door a little bit open, and close it repeatably. From this you will hopefully be able to get your hand out the door to clear more snow. From that you can then open it even more. Repeat this process until you can fit a shovel out to clear the door.
In the future it would be better to open the door every few hours so that the buildup of snow is less at each time and only swinging it allows it to open.
An alternate option is to open your garage door as it is vertical and will not be blocked by the snow.