Apple Watch help!

If I have straight talk can I use an Apple Watch and what all can I do with it if so? Do I need to purchase an additional plan to make the cellular feature work? I want to get the watch to be able to text and call without my phone! What do I need to be able to do I have so many questions and really wanting to get a watch for me and my fiancé both but need to know a few things before I decide to purchase!