The Rails are basically narrow, yet flexible, metal bars that the users can only just fit their feet on. The finer design details vary between games. By jumping onto the Rail and balancing on top of it, the user can slide down it at moderate speed. When using the Rails, sparks will fly from the user's shoes as they grind.
In gameplay, Rails are used to reach new, and often inaccessible, areas by creating paths for the player to travel on over grabs otherwise too wide to be crossed normally. When using them, the playable characters grind down the Rails to area they lead to. Additionally, the player can grind both uphill and downhill on them without losing speed. To utilize a Rail in gameplay, the playable character just has to jump/run onto it. While grinding, the player can jump and perform certain moves, like the Dash. The only way to get off a Grind Rail is by grinding/jumping off it at its ends.
Some Rails are connected to the ground at their end points, while others simply float in midair. There may also be objects along the Rails that the player can pick up while grinding, the most common of which are Rings.
Sonic Boom: Shattered Crystal
Rails appear exclusively in almost every adventure level, the last of which focus readily on jumping/swinging between Rail sections as the player moves forward. Sometimes, there are dash blocks blocking the Rails at their starting points, just above pits, forcing the player to use the Air Dash at the right time.
Sonic Dash 2: Sonic Boom
In Sonic Dash 2: Sonic Boom, Rails are thick and light gray with a more high-tech look, possessing black and red sliding frames and a light blue-glowing top surface. In this game, Rails always appear in sets of three, with each Rail running parallel to one other. Along the Rails, the player can pass through Hoops and pick up various powerups, Orbs and Red Star Rings.
Rails are mostly set on the ground. Some are also floating above the game's primary track, which can be reached with Springs, although they will inevitably end and make the player fall down on the road again. In gameplay, the playable characters can also jump between parallel Rails when the player swipes their finger across the screen towards the desired Rail.
Sonic Boom: Fire & Ice
In Sonic Boom: Fire & Ice, the Rails look just like they did in Sonic Boom: Shattered Crystal, except their bars are light blue and the their binds are orange (matching the game's central theme about fire and ice). The game also introduced spiked blocks that appear along the Rails, some of which move in on the characters when they get close, which the player can dodge by jumping over them.