What action allows you to charge expenses to a project?

The ability to charge expenses to a project specifically involves linking or associating those expenses with the project in question. Attaching expenses to the project ensures that the costs incurred are tracked and accurately reported within the project's financials. This action allows for proper budget management and financial analysis as it provides visibility into how much a project is costing and where those costs are allocated.

While adding projects manually could enable the creation of a project, it does not address the financial aspect of tracking expenses. Creating expense reports is a broader activity that involves summarizing expenses but does not directly tie those expenses to specific projects. Reviewing the project timeline is focused on planning and scheduling aspects rather than financial management. Thus, attaching expenses is the key action that allows for the financial accountability needed in project management.