For now, the ablative is used to show how something is done. It is usually the object of certain prepositions, but it can be used alone in Latin to express the means used to do something without a preposition.
I ran over a bird with a car.
"With a car" show how I ran over the bird. In Latin, the preposition "with" when it means how, can be translated by a word in the ablative case without using a special preposition. In this sentence, it would be translated carro. This is called the ablative of means.
The ablative endings are included in this chart. Notice their position in the chart.
*Notice that this ending should have a long mark.
Don't stress about the -is endings. You can tell which one you use by looking at the verb (remember that datives have to follow verbs of giving, showing, or telling). If you don't have that, you probably have an ablative. The gender will be based on the nominative of the word. I will explain in class more.