In the diagram if 1 square is equal to 10N (10 Newtons) then arrow a shows a vector of 40N to the right, and arrow b shows a vector of 50N to the left.
ALWAYS USE A PENCIL AND RULER WHEN DRAWING ARROW DIAGRAMS
Always make sure your diagram is the correct length and include a scale to show how much force each centimetre in your diagram represents (for example 1cm = 10N)
Here you can see 3 examples of combining vectors together. The top one adds vectors that show forces acting in the same direction (added together). The middle diagrams show two forces acting against each other (in opposite directions) so they are subtracted. The bottom diagrams show two forces acting in the same direction and again being added together.