Hi U U,
1. If the noun is singular, you would translate the sentence as "There is", if it is plural as "There are":
a) Es gibt ein Auto. = There is a car.
b) Es gibt Autos. = There are cars.
2. You need to add "da" to get a meaning which is roughly similar to "Es gibt":
Es gibt Autos. = Es sind Autos da.
You can replace "da" with any place to make the sentence more specific: hier, in der Stadt, zuhause etc. There is a slight difference: "Es gibt" emphasises that something exists, "Es sind ... da" more that you have these things or that they are close by.
3. Nein, das ist leider nicht richtig. The same rule as above applies, "Es gibt" roughly equals "Es ist .. da" but with the same slight difference in meaning as described in 2.
I hope that helps.