A company generates cashflow based on its day-to-day operations. Eg. SIA selling air tickets with fuel surcharges 2x actual ticket prices. The millions of ticket sales generate cash. Of course SIA needs to pay the pilots, the stewardesses, the fuel, landing charges etc. After netting the expenses, it should still have cash left. Some co.s don't, if you own some of these, good luck! Anyways, this no. is called Cashflow from Operations.
Next, SIA needs to spend some of this cashflow on equipment to maintain its operations. Like buying new planes, pilot training programs, etc. This no. is called Capex which is the short-form for capital expenditure.
When you deduct Capex from Cashflow from Operations, you get a no. called the Free Cash Flow. Basically, that's what's left that can be distributed to shareholders or to pay down debt. If the company has no debt, it's basically money that can be paid to the shareholders.
Over the course of many many years (like 10 yrs or more), a good co. will generate significant Free Cash Flow and has the capacity to even grow this amt over time. Now finally, things are getting interesting right? These are co.s that value investors look out for. Usually, I would look at that past 10-15yrs of FCF and take an average amt to use that to calculate EV/FCF. I am assuming that the company can generate this average FCF in the future for many many years.
Let's look at SIA. Over the past 10 years, SIA has 5 yrs of positive FCF and 5 yrs of negative FCF. Cumulatively, it generated a miserable S$175mn of FCF. Our ministers' salaries over 10 years would have generated as much. This is what the most profitable airline in the world can manage. Moral of the story: Don't ever buy an airline!
Combining the two things, you get EV/FCF which is just a measure of the cheapness of the company. The lower the better, like the PE ratio. If this ratio gives 5x, it means that theoretically, you get back your money in 5 yrs. Usually it doesn't get cheaper than that. EV/FCF ranges from 5-15x usually.
Again, back to SIA, the EV is S$8.8bn based on current stock price of S$11+. Calculating EV/FCF give 8800/175 = 50.3x. If you buy SIA today, the free cashflow generated should be able to cover your purchase in about 50 yrs. That's great isn't it? Maybe just in time to cash out and pay for the funeral expenses!