This Japanese spinning top consists of four parts. There is the top itself, the wooden base that you spin it on, and then two thin wooden discs.
The wooden discs are placed within the base, leaning against the edge of the top. Because the two discs have slightly different diameters, they rest against the top at slightly different angles, and - when the top id spinning - this causes one of the discs to revolve faster than the other one. So every so often, one of the discs overtakes the other one. Or rather 'undertakes' since it passes underneath the other one.
You can place the top and the two discs in position, and then spin the top. Or you can spin the top first, and then place the discs into the base while the top is spinning.
The design on the discs varies, but every top will have two discs with different designs.