The internal router settings dialog is shown below
.
Track
Width - The default width for tracks. You can override this by setting the width for the track/net using the tracks properties box.
Spacing - The spacing between tracks. The internal router is a grid router and this is the size of the grid.
Grid
Track - The internal router is a grid router and this is the size of the grid for tracks.
Via - This is the size of the grid for vias.