From the left side of your wp-admin page click on Products then choose Add Products or select the product you want to edit.

Center Column

1. Add Product Name
2. Ignore the main text widow
3. Fill in Product Short Description

Center Column > Product Data – Simple Product

1. Choose Simple Product from the drop-down menu
2. Select the General tab
3. SKU and Price must be filled in
4. Select the Inventory tab
5. Confirm Stock status is In stock
6. Select the Shipping tab
7. Input Weight and Dimensions
8. Apply a Shipping class (I have defined this on Products > Shipping Classes and set the cost of each rate on Woocommerce > Settings)
9. click on the Shipping tab then click the link Flat Rate below the tab.

Center Column > Product Data – Variable Product

Use this if the product has variations such as different sizes or colors.

All of the above Product Data for a simple product still applies.

1. Choose Variable Product from the drop-down menu
2. Select Attributes
3. Click the Add button for Custom Product Attributes
4. Name the attribute and give it values separated by pipes. i.e. Small|Medium|Large
5. Check the Used for variations box
6. Select Variations
7. Choose Add Variations and click the Go button for each variation
8. Choose a default variation
9. From the drop-down select each variation
10. On the right of the drop-down there are 3 options. The three bar icon is to arrange the variations. Up arrow is to expand the variation window to edit options. Remove should be clear.
11. Click the expand icon
12. Price is  the only required field

Right Column

1. Select all applicable Product Categories. (These are defined under Products > Categories)
2. Enter Product Tags. These are keywords that will help filter this product
3. Upload your product image. Images should be at least 1000×1000 pixels. Square is easiest to manage.
4. If there are multiple images add the remaining images to Product Gallery. You can move these images to rearrange.