Take all the shares of a company and multiply this by the market value of each share. This is the total worth of the company in terms view of its current (stock) market valuation. Answers appear in Millions/Billions of Dollars. It is not company profitability, nor the original amount subscribed for the shares.
How much is a company worth today? The value of each share is set by how much someone is willing to pay for it, and is influenced by supply and demand for shares, and the performance of the company. Total Market Capitalisation is the worth of the whole company calculated by taking share price of one share and multiplying it by the number of the shares the company has.