The game is set with an overhead view of all the action. Unlike other Bill & Ted games, players get the choice to play as either Bill or Ted.
The main aim of the game is to collect all the musical notes that are scattered around each particular time. The game starts with the player having access to only one timeframe - old Egypt. Bill and Ted can travel to the next timeframe by collecting 16 musical notes, or a phonebook page.
There are different structures in the game that can be entered to collect notes, keys, or other important items that are needed. If the player is touched by an enemy, the character is respawned at the entrypoint of the last building or back at the phonebooth.
One interesting gameplay feature is being able to use different items and instruments to ward off enemies. The player starts with the guitar, and if they collect and switch to a different instrument, the game's music changes to reflect the instrument that is being played.
Another interesting part of the game is the interplay between eras - for instance, when in old Egypt, the player is warned that one of the items they see (the staff) has a false version and a real version. After the player travels to ancient Egypt and finds the staff, then gives it to its owner in old Egypt, they cannot travel to the next destination until they plant the warning. This avoids a time paradox.
Players can save their progress by a unique 16-character password, which represents every part of the game's state. This system worked very well and saved on the costs of putting non-volatile memory into the Lynx game card. It was also possible to play a cooperative multiplayer game, with one player as Bill and the other as Ted, by use of a ComLynx cable.
Source: Wikipedia, "Bill & Ted's Excellent Adventure (Atari Lynx video game)", available under the CC-BY-SA License.