A power of attorney is a legal document that enables you, as the principal, to appoint a person you trust, called an agent, to act on your behalf. Customarily, this would entail the agent performing financial tasks or making healthcare decisions for you. You can draft the document to be sweeping and give the agent authority to do nearly any financial task you have the right to do, or you can limit the authority to a specific task, such as paying your bills from your bank account.
You should also consider whether to make the document durable, meaning that it would continue to be in effect after you become incapable of making decisions, for example, because of dementia. In Virginia, powers of attorney are not durable unless you explicitly state so in the document.