Fix It is a puzzle game where the player assembles various machines out of a kit of spare parts. The machines are similar to Rube Goldberg devices and involve releasing a bolt from a wrench and then have it reach a box. For each machine the player has access to a toolbox with a certain amount of components of various kinds that have to be placed on the playing field to complete the machine. Most common are the elbows (l-shaped pipes) which change the direction of the bolt and the converters which change the property of the bolt. The bolt can be small and hollow, large and hollow, small and solid or large and solid and these properties have to match with the properties of the box and the parts. For example, to reflect a small and hollow bolt only an elbow with those properties will work. There is also the bouncer which rebounds the bolt in the opposite direction and the key which the bolt has to pass through to enter a locked box.

The game consists of 200 machines. The first 100 only uses regular parts while the latter 100 contains modified parts. These differ in that their properties change every time they are touched by the bolt. The parts can also rotated and change position. Machines can be built in any order even if previous ones have not been completed. Additionally there is an editor that allows the player to create new machines.