If you had one of the older Microsoft Windows versions, than you might remember the game Minesweeper. You had to find the mines and avoid them by marking them. It worked with some clues, since numbers gave away how many mines are close by.
The Hexcells games are very similar to it, but they are not working in square blocks, they come in hexagon shape and often remind of chemical combinations when you open the next level. These shapes make it sometimes hard to figure out what is going on and in later levels you get extra clues for the lines of hexagons and stuff like that.
playing Hexcells is fun in a kind of weird way. Even if you don't want to make your math homework, you sit down to "calculate" the grids, but it is not that much math anyway, more like drawing lines from dot to dot.
Later versions of Hexcells (Hexcells Plus & Hexcells Ininite) are basically the same thing on harder levels and Infinite includes an Endless-Mode that let's you play levels created by chance. Start with the normal game and get infected, this game is addictive and you should consider buying the complete pack right from start.
10/10 I think I've seen more hexagons than a beekeeper did