You can read about what it does here.
However, it doesn't work the same for everyone. Some women respond better than others and you have to find the right dosage for you. I have PCOS and only was having about 2 periods a year and wasn't ovulating. I started 500mg of Metformin on January 30th this year. A week later, I went up to 1000mg and then at the end of February, I went up to 1500mg. It has been great for me. Since January, I have lost about 15-20 pounds. I get full faster and feel alot more normal as far as eating goes. Some women don't get their period with just Metformin but I thankfully did. I got my period 53 days after I started Metformin and ovulated on day 42. It's the first time I had ovulated on my own in about 5 years. Getting pregnant on Metformin all depends on if you ovulate or not. You can get your period but not ovulate. If it brings on ovulation for you, then yes you can get pregnant. Some other things you may want to look into and ask your doctor about is Femara and Clomid to bring on ovulation.
I will warn you though that until your body adjusts, the side effects are awful. I was having to run to the bathroom all day. After a week or two though, it's fine. But again, everyone reacts differently.