From Dashboard
- Woocommerce
-Coupons
-Add Coupon
-Enter Coupon Code (IE WELCOME10)
-Select Discount type (ie Fixed Amount or Percentage)
-Enter Amount
-Set Expiry date
-
-Update Usage Restrictions (optional)
- Minimum and Maximum spend
-Assign / Exclude certain Products or categories

Update Usage Limits (optional)

Once all details confirmed click Publish