As ezdays said it will take some practice. I find that solid core wire rather than stranded works best. The solid core wire can be bent, "L" shaped to fit in along the outside of your rail. Offset the "L" slightly and it will lay in position, or you can hold it in place with a small wooden probe. As ezdays mentioned, it is important to pre-tin your lead end with solder Add a little flux to the rail, pick up a little solder on the tip of your iron and the solder should flow nicely along the area where you added the flux. An old trick I learned was that little wads of wet tissue make great heat sinks. Wet several balls of tissue, about a half inch in size, moist but not dripping with water and mush them down over the track about three quarters of an inch on both sides of the area you are about to solder. Don't forget to clean your solder joint of flux with a little alchol. A good solder joint will be bright and shiney not dull and crazed. Good luck.