Carbon credits can be bought and held in a registry. Then they can be transferred to someone else (as a gift or a sale) or retired.
If you choose to hold or sell credits that you own, you can’t then also use them to offset your own carbon footprint, because that would be double-counting.
If you want to offset your own carbon footprint then you have to retire your credits – once retired, carbon credits can not be traded.
When you choose to retire some or all of your carbon credits, Credible Carbon issues you with a downloadable retirement certificate, so that you can substantiate your offset claims.