E.T. is an adventure game in which players control the alien E.T. from a top-down perspective. The objective is to collect three pieces of an interplanetary telephone. The pieces are found scattered randomly throughout various pits (also referred to as wells). There is no overall time limit.[8] The player is provided with an on-screen energy bar, which decreases when E.T. performs any actions (including moving, teleporting, or falling into a pit, as well as levitating back to the top). To prevent this, E.T. can collect Reese's Pieces, which are used to restore his energy or, when nine are collected, E.T. can call Elliott to obtain a piece of the telephone, or the player can save the candy pieces for bonus points at the end. After the three phone pieces have been collected, the player must guide E.T. to an area where he can use the phone, which allows him to call his home planet. Once the call is made, a clock appears at the top right of the screen; E.T. has to arrive at the landing zone before it reaches zero.[9] Once E.T. gets to the forest where his ship abandoned him and stands and waits in the designated area for the ship to come, the ship will appear on-screen and take him back to his home planet. Then the game starts over, with the same difficulty level, while changing the location of the telephone pieces. The score obtained during the round is carried over to the next iteration.[10] E.T. has three lives and if he dies within those three lives Elliott will come in and revive him. E.T. can get a fourth life if the player finds a geranium in one of the wells. According to the manual, the game ends "when E.T. runs out of energy or when you decide to quit playing".[9]
The game is divided into six environments, each representing a different setting from the film. To accomplish the objective, the player must guide E.T. into the wells. Once all items found in a well are collected, the player must levitate E.T. out of them.[11] An icon at the top of each screen represents the current area, each area enabling the player to perform different actions. Antagonists include a scientist who takes E.T. for observation and an FBI agent who chases the alien to confiscate one of the collected telephone pieces, or candy.[10] The game offers diverse difficulty settings that affect the number and speed of humans present, and the conditions needed to accomplish the objective.