Hi. It is a true gar species, most likely a Florida gar. They will get 18-24" in captivity, so you will need a large (100+ gallon) tank in the future. How long is it now? You should expect it to hit 12" in about 6 months time.
Was it feeding at the store? If so, keep feeding it whatever the store had it on. Otherwise, start it on live feeders (rosy red minnows make great feeders). Keep it well fed, every day. Once it gets larger you can try getting it to take shrimp, fish fillet, krill and pellets.
Welcome to the addiction!