You will likely pay a retail purchase fee (typically between $1.95 and $5.95) plus the initial amount you want to load onto the card.
If you must use a credit card to fund your Green Dot account, there are a few indirect paths, though they often come with high costs: buy greendot with credit card
Handing cash to a cashier at a participating Green Dot Network retailer. You will likely pay a retail purchase fee