total revenue & marginal rev.

Marginal revenue product (MRP) is the additional revenue to a firm from using an extra unit of a factor. Be careful that it is not the same as marginal revenue (MR). MR is the additional revenue from selling an extra unit of good.

Suppose that employing an extra unit of a factor produces 500 extra units of good each month. MRP is the additional revenue from selling that 500 units of good.

Suppose the wage rate is determined externally. A firm will employ a factor up to where MRP = wage. When MRP is greater than wage, the firm will gain by employing another unit of the factor because additional revenue (MRP) is greater than additional cost (wage). When MRP is smaller than wage, the firm will decrease employment of the factor because the extra revenue from the factor (MRP) is higher than the wage it has to pay.

When the firm sticks to the rule that it employs a factor up to the level where MRP and wage is the same, the MRP is the firm's demand curve for factor.

To answer your question, MRP is not the wage of a factor but a firm will employ a factor at the level where MRP = wage.

Let give an example on sales. Total Revenue means the total amount you received from selling the goods. Marginal Revenue means the additional amount you received from this additional.
For example, you can get a sales of $100 for selling 10 pcs of $10 each. This is the total revenue. You will get an additional $10 or even $11, an increase of selling price, for selling an additional item. This is the marginal revenue.


For simple idea and calculation, see

http://ingrimayne.com/econ/elasticity/TRMRques.htm

For elasticity, total revenue and marginal revenue, a very good explanation and graphical presentation, see

http://www.economics.utoronto.ca/jfloyd/modules/eltr.html