Hi: Contining with my sweater… I need to start another ball - same colour. Do I just drop the end of the ball that has ended (leaving a tail) and pick up the end of the new ball and leave a tail?
Yes. You can either just leave the ends hang or tie a loose knot to keep them together - weave them in later (take the knot out before weaving if you do that). Or, if your yarn will hide it, you can knit it in for a few stitches and trim it off (make sure you cut the right one!).
I ties my ends together loosely, then when I’ve knit a few more rows, go back and readjust the knot so it’s on the back side. Contrary to what some people say (don’t make a knot, it’ll show, work it’s way to the front, etc) mine never do. And I knit at a loose gauge.
I do something called a Russian join. That way, I never have to weave in ends. It can be used with two yarns of the same color or two of different colors. You use a needle to thread your working yarn back through the center of itself (when you have just a bit of a tail left) to make a loop. Leave enough of a tail sticking out of the yarn so that you can tighten the loop. then put yarn number two through this loop and either thread it into the center of itself and tighten both loops down (think of this as making two links of chaing fastened together) or just hold the two ends of that yarn together for a few stitches and tighten the other loop. You can google it and see pictures if you are interested. I hate weaving in ends and avoided multi-ball or multi-color work at all costs until I discovered this one.