A 4x4 foot garden bed, for example, will have 16 planting squares (because there are 16 square feet in a 4x4 bed). A 4x8 foot garden bed will have 32 planting squares.
For instance some companion plants for your tomatoes are onions, carrots, and parsley while cabbage and cauliflower need to be kept away. Be sure to rotate your vegetables every year, if you planted tomatoes in the green bed last year plant them into the red bed this year.
This type of planting will discourage insects and specific vegetable pathogens that can stay in the soil over winter and planting that same crop in that bed will infect the crop.
Each planting square has an address used to identify the square. While the methods for addressing vary, one of the simplest is to use letters for columns and numbers for rows, and the combination of the two identifies the square.