This is it, putting the cutting in soil. After this it's just maintenance, water, food, all that.
So here's the cutting that I took about three months ago. Good roots, it's ready to go. Just fill a starter pot ~1/3 full of soil. Put the cutting down carefully, try to get the roots as evenly spread out as possible. Now carefully cover it with more soil, water it well and put it in bright indirect sun. You won't need to water it much for the first few months (over watering leads to root rot, repeat as needed for emphasis), it takes a while to get a good root system, but keep an eye on it and don't let it dry out all the way.
And that's that. Now bear in mind, ficus benjamina doesn't grow very quickly indoors. I have a small tree that I started a couple years ago that is still only ~1 1/2 feet high, so don't expect anything too drastic. I've found they tend to grow in spurts, putting out a few new branches/leaves all at once, then going dormant for a couple weeks, then doing it again.
Here are the other ficus benjamina propagation post:
How to Propagate Ficus Benjamina: Part 1
How to Propagate Ficus Benjamina: Part 2