kellimath,
Hello and welcome to the forum. I don't grow
F. nitida but I do have some
F. benjamina and I imagine care is pretty similar. First, don't put too muck stock in the tag that came with it. Second, remove the glued on pebbles. This is important so that the tree can breathe properly and so that you are able to better judge when to water.
it appears to me that some thin branches have been brought down and are anchored under the moss somehow.
These sound like aerial roots that Ficus sometimes develop.
[img]https://www.artofbonsai.org/galleries/images/jim_smith/jim_smith_ficus_retusa.jpg[/img]
I need to know HOW AND HOW MUCH TO WATER
Proper watering is not so much about quantity, which should always be sufficient to thoroughly wet the soil, as much as it is about frequency. Always water generously but the real issue is how long to wait between waterings.
Ficus are fairly forgiving in this regard. If the soil is approaching dryness it is time to water. Check beneath the surface, not just the top. A small dowel rod or chopstick can be inserted to the bottom of the pot and left there. Check the stick every day and if it is dry then it is time to water again.
I have my Ficus outside in full sun and we have had temps in the 90's here. Ficus like warmth and humidity but adapt well to indoor conditions that is why they are marketed as indoor trees, which is something of a misnomer as no trees evolved inside.
Your tree will do fine outside, with one caveat. Since we do not know what conditions it was recently exposed to try to find a semi sheltered spot at first. A spot that is sheltered from the hottest afternoon sun will be ideal for now. Once you are comfortable that it is doing well you can gradually expose it to more sun. Some Ficus tend to drop their leaves when exposed to a different environment but most always recover.
Ficus will not survive very low temperatures so if your area gets below 50F for extended periods it should be brought inside during that period.
Please post pictures if you are able and if I missed anything don't hesitate to inquire further.
Norm