The yoke is the part of the sweater that lies across the shoulders. As I understand it, you're now oriented the same way as the diagram. The back of the sweater is on the left. The front is on the right. The second front (the left front) just has 3rows knit and it's at the end of the needle farthest from the point. The back is on the needle nearer the point of the needle. If you have the working yarn coming off the back at the needle tip you can knit across the back, drop the yarn, pick up the working yarn for the front and knit across the front. Do this for 2.5 inches and then join back and front with one strand of working yarn.
If your working yarn isn't coming off the ends of the back and front nearest the tip of the needle, then you need to slip off them that needle onto another so that the working yarn is in the correct place to knit with.
The 5 inches is measured from one end of the neck slit to the other so that includes the 2.5" you've already knit.