This tapestry crochet tutorial has step by step pictures showing how you can crochet circles / dots. Tutorial also has free pattern.
My previous post might help if this is your first attempt at tapestry crochet – Introduction to tapestry crochet for beginners.
Here is the chart for this pattern. You can pin it for future reference.
Make a foundation row of chains (multiples of 10 +1). For next row, green yarn will be carried into the single crochet stitches.
To change color, when there are two loops on the hook, yarn over and pull green yarn.
Add required number of green stitches.
Second row is a repeat of the previous row.