Your monthly financial report should contain at least two statements - a statement of activities (known in the for profit world as an income statement or profit and loss statement) and a balance sheet.
The balance sheet provides an overview of what an organization is worth. It outlines how much money is available in bank accounts and other investments, the value of property, furniture, and equipment, accounts payable, other debts and liabilities and net assets. Net assets are divided into:
Unrestricted funds were available to the organization to spend in the fiscal year covered by the statement.
Temporarily restricted funds were promised or awarded in the year covered by the statement but they were given to the organization for it to spend in the future or for a specific task that isn't yet complete.
Permanently restricted funds were given to the organization for permanent investments - such as endowments. Earnings on such money may be used toward the organization's costs (your board will set a policy about how much of these earnings may be used), but the amounts donated as restricted gifts shouldn't be spent on current activities.
The statement of activities outlines "Revenues and Expenses" which tell you how much money the organization received in the past year, its sources for that income, and how it spent that income. The statement of activities also contains a statement of functional expense, which details expenses spent on programs and those expenses that were exclusively for general and administrative costs and for fundraising costs.
The statement of activities should also include a comparison to budget. As a board member reviewing the financial statements you should be asking questions about line items (ticket sales, salaries, marketing expense) where the actual results are substantially off from the budget in either direction. Expenses being less than budgeted are not necessarily a good thing - it may mean that critical planned tasks have not been completed.
In reviewing the balance sheet, you are concerned with the cash balance and whether there is sufficient cash to pay existing invoices and other expenses expected in the near future. Most smaller choruses will not have permanently restricted funds but you do need to be careful about temporarily restricted funds. Many foundation grants are for specific purposes rather than for general operating use. Such funds must be accounted for as temporarily restricted and the use of these funds must be carefully monitored. While you may not need to be involved with the accounting details of temporarily restricted funds you do have an obligation as a board member to know that temporarily restricted funds are only being spent on the activities they were granted for.