most computers have an integrated GPU in the cpu, this one is very weak.
Game computers also have an separate GPU from either AMD or nvidea these are suppost to be very powerful. If you have one you want that your games use this one instead of the integrated GPU.
which gpu is used is normaly decided by your computer and usually it got it correct.
Minecraft however is made in such a way that it is seen as a program that doesn't need the power the other GPU uses and thus most of the time it will use the integrated GPU this will result in bad fps or at least worse then when it uses the dedicated one. You can however change its default behavior to fix this.