When you load a markbook you will be presented with the pupils along the top of the page and the objectives down the side. Each pupil has a tile for each objective where their current assessment judgement is recorded. All assessments are automatically saved once they are made.
Click and Colour
Select the tile(s) you want to change by clicking on them. When clicked on they will highlight grey with a red border:
Click the level of assessment you want to give to the objectives from the palette in the top left hand corner and the tiles will change to the selected colour:
Paintbrush Mode
Click the paintbrush icon in the top left hand corner and then the assessment level you wish to apply: