Click a segment line to toggle curve marking. You'll be prompted to select a speed limit when creating curves. Click on numbers to move all numbers for that curve left/right.

Racing Kerbs
Add red & white striped kerbs to track borders. Click on track borders to add/remove kerbs on that side.

White Lines
Add white lines to track borders (grouped by target curve). Click on track borders to add/remove/switch white lines.

Edit Segments
Drag and drop segments to reposition them along the track. Click and drag segment numbers or lines to move them.