is the thread that has a comprehensive guide to betta keeping. I suggest you look there for tips from the experts!
And welcome to the betta keeping hobby! I'm a newbie too :D
That liquid could be anything from stresszyme, to water conditioner, to aquarium salt. Make sure you do use water conditioner though that detoxifies chlorine, chloramine, and ammonia from tap water. Also, what size tank is he in? Most of those starter kits are horrendously tiny :( Most people here recommended a 2.5-5 gallon minimum for bettas. I personally have a 2.5 gal and my Xander is quite happy in it.
Bettas also need to be kept in warm water, so make sure your water is always stable and between 76-82 degrees. To keep it there, you will probably need a small heater.
But those are just the very very basics, there i SOOO much more to learn! Check out that other thread to find out exactly what you need - and have fun! Bettas are wonderful pets and can be quite entertaining and fun when maintained properly