Further to this, I would suggest that track (especially modern Nickel Silver stuff, which I've found much harder to solder than steel) is not the best place to learn to solder. It's very easy to melt the sleepers if you get it wrong (and if you're doing it for the first time, you probably will) and any problems not spotted at the time will (as mentioned above) become a nightmare later on. When I relearned to solder (I had previously done it once at school the best part of five years beforehand) I practised on an old Hornby Hymek (the clips that connect the wires from the pickups to the motor had expired). This is the sort of thing that I would encourage a newcomer to start on - it's unlikely you'll melt anything, and if you do it will probably be hidden once you put the body back on.
Plus, if you don't make a good connection on your first attempt, it's far easier to recitfy the issue than it would be if something went wrong with the track. And if things really go wrong, you lose* one loco, and don't have to rip up all the track and start again.
*When I say lose I, remember that if the damage is mechanical or electrical you can just disconnect the motor from the pickups (if the damage is electrical, that last point may be redundant), remover the gears, and run the loco in double-headers, and if the damage is cosmetic, you can use the motor etc. for spares and the body for painting practise, if that sort of thing takes your fancy.