It's been a while since I've played. I don't recall if you can buy a turret for a Tarsus, but I'm pretty sure you can't. If you can you have to buy the turret and then a tractor beam for your ship. Once you have one, the easiest thing to do. Is head towards the object you are tractoring. Start slowing down as it starts to appear and grow in size in your viewscreen Come to a complete stop when it is rather large. I think the first ship you can afford with turrets is the galaxy which has them on the top and bottom. After your ship has come to a stop, point the nose of your ship down, so the object goes off the top of the screen. Switch to the turret, cycle the guns using the G key to bring up the tractor beams and hold down the button you use to fire your guns. the object will be dragged into your ship. Return to the cockpit view and continue the mission.
As for making money, different people have different views on this, but I've always started off with a couple lasers and a missle launcher with the FF missles. Once you can afford it 2 missle launchers are better. There is a mission computer on all bases and planets and you can hire yourself out to fly missions. Early on, just choose the ones that place in the Troy system. When I have enough money, I join both the Mercenaries and Merchants Guilds. The jobs they offer pay more. Try to take as many missions as you can in the Troy system at the same time (a maximum of three.) You make more money faster.
At this point I also try to upgrade to Meson Guns, buy 2 launchers, fill them with FF missles and buy a repair droid. (A note about the repair droid, make sure at the end of a mission before you land you let the droid finish making repairs to the ship, otherwise the dealer will offer to fix them for you and that will cost additonal money. There are a few things, like armor the droid doesn't fix, but he is handy to have and will save you money in the long run. Keep flying local missions until you can afford a Nav map and a jump engine. Go ahead and buy the full nav map, the others aren't worth the trouble, in my opinion. Also you can start your missions on one of the Steroid bases In Troy and end up on the Planet Helen. If you have some spare credits, buy some food and sell it back on the bases, you can usually make some additional money that way.
Now that you have a jump capable ship, start looking (first in the Merchants Guild) for missions to New Detroit invovling shipping ore. Try to find three of those (which sometimes isn't that hard, there may be some in the regular mission computer as well) If you have any spare credits, buy ore of your own from the commodity exchange and head for New Detroit. Oh, one other thing, buy an afterburner. In this game especially early on, it does hurt to run away and live to fight another day. The nice thing is you can AB to a jump point and as soon as you are in it, you can hit the J key to jump. If your pursuers are well armed or close tehy can ding you up a bit before the jump completes.
At this point, I start making runs between New Detroit and some of the mining bases, buy better sensors and then save up my money for a Galaxy. The game is a little tricky at first, but once you get a decnet ships with some cargo space and some weapons, it is a lot of fun. I've stuck a link at the bottom of this note that has some more info that might be of use to you.
Good luck!
http://members.xoom.com/smaruska/weapons.htm