Net metering describes the option of having a two-way electric meter that records both power that you get from the grid (and would have to pay for), as well as excess power that your solar panel system generated that you did not use and that got put into the grid instead.
Then, if the excess generated and put into the grid is more than you got from the grid, you will have eliminated your electric bill and have to get a credit for future electric power you may later use, or actual payment for the excess power generated!
If you got more electric power from the grid than the excess that you put in, the amount you put in is subtracted from the amount you got, to arrive at lowering the total of the cost of your bill, as you have offset and erased some portion of your bill through generating extra power, more than your own needs, and sending that power to the main grid.
Feed In Tariff (FIT) is a different way to get paid for the excess electricity generated by your solar photovoltaic PV system. Getting paid under the Feed In Tariff means you are signing a contract for a fixed period of time (usually 10 years, or 20 years, or 25 years), during which you are to be paid an exact fixed amount for each kilowatt-hour (kWh) of energy generated by the solar panels of your solar photovoltaic PV power system that you do not use and that goes into the grid.
For example, in California, choosing the Feed In Tariff in 2012 had the options for a 25 year contract paying 9.27 cents for each kWh generated, or a 10 year contract paying 7.68 cents for each kWh generated.
These rates are paying roughly half of what it costs the average homeowner to purchase electricity.
The Feed In Tariff is generally recommended for people who are operating a very large size solar power system with so many panels, that few private homeowners choose this option.