The grids are the vertical lines in the Composition area which let you see the bars, or beats, of your project. In some cases you might need to zoom in to get a clearer view of what you're doing.
There are three ways of zooming in and out:
a) Use the magnifiers in the lower right corner in the studio (1). Zooming in automatically adjusts the grid resolution to match your zoom level.
b) Use Cmd/Ctrl+arrow left/right if you like zooming using keyboard shortcuts. This is probably the fastest way to work!
c) Use two fingers to zoom in and out if you have a touchpad!