The answer is that for now, you should not be pruning anything if you are just starting bonsai. The first 6-12 months should be spent learning how to keep it alive. The average life-span of gift-bought bonsai for beginners is about 6 months, so really do read up all you can.
Your ficus can tolerate indoor conditions. Put it in good light, on a gravel tray to raise humidity. Watering bonsai is massively important. Incorrect watering is the number 1 killer of bonsai.
You need to wait until the soil has dried out slightly. Don't keep it moist at all times, let it go a bit dry without drying out completely - you will learn this with practice. Water once, very thoroughly, saturating every bit of soil in the pot and letting it run out of the bottom of the container. Leave for 10 minutes, then repeat. The first watering increases the water-holding capacity of the potting mix. The second watering gets water to all of the roots. I see in the pic the edges of the potting mix are dry. Ensure every particle of soil is wet after watering lol.
As for fertilizer...your tree will survive, but not thrive, if not fed. During the winter months, feed every 4 weeks. Buy a bonsai one if possible, or just use a regular house plant fertilizer at half strength. During the summer and spring, use fertilizer every 2 weeks, again, either a bonsai one or a regular one at half strength.
Your ficus is the same type as mine, and is thankfully a good starter tree. They can usually tolerate less-than-perfect-care while you are learning. The light, humidity and watering are massively important. I would suggest reading up as much as you can on bonsai, buy books, or join a local club. It sounds like a lot for such a little tree, but if you want to keep it alive, and follow bonsai as a hobby and art, it takes a lot of time and effort to get going. If you get enthralled with bonsai like so many do (:D) you will end up with more than one! Once you have got the care under wraps, its really easy to take care of them.
I hope I haven't put you off with this long reply lol. Its just that I like seeing enthusiastic bonsai beginners, and its always really nice to see someone care for them well and continue caring for them. I would recommend visiting the site below, joining it, and going into the 'help for beginners' forum. You'll find a wealth of info!