No matter how simple you think your game is, having some sort of user on-boarding is important. For our Plug It In game we were able to accomplish this in less than 10 seconds.
It accomplishes the basics: 1) Match the plug and 2) Match all before time runs out. Another important aspect is that there is that the game does not “reset” after the tutorial. You progress to level 2. This gives the user a sense of accomplishment while learning.