Here you control how the particles will be displayed in the viewport.
Visible
Toggle the particles' visibility in the viewport.
...
Determine how many particles you want to display in percent. This parameter does not influence meshing or rendering, and has no effect when instance objects are displayed (see Fluid > Particles > Render Only).
Size
The particles' viewport size is adjusted here – rendering is not affected by this value. Valid settings range from 1 to 100.
...