When you solve a rubik's cube, the goal is to get all of the pieces in their correct positions and oriented. It takes some practice, but eventually you can achieve it. In fact, the current world record for a regular cube is 4.90 seconds set by American 14-year old Lucas Etter. But how many moves does it take to make a good solution? A lot of work and maths have gone into answering this question, which is what's called a "NP-complete" problem — that's maths lingo for something even professional mathematicians have trouble solving. It took more than 30 years, but finally, scientists have determined that any scrambled cube can be solved in a maximum of 20 turns.
This is a great result. It means that any person on earth can solve a rubik's cube by memorizing the steps of an algorithm — sequences of turns to position a specific piece (say, a corner) before moving on to another, until all the pieces are in their proper positions and orientations. Generally speaking, an expert would use more than just twenty moves to solve the puzzle, but these steps are easily memorized if you know what to do and how to do it.
The actual number of moves will vary depending on the algorithm and the position of a given piece, but the general rule is that there are always lower bounds on the number of moves needed. For example, the lower bound for a face-turn metric is 20, and the upper limit for a quarter-turn metric is 26.
