Newbie questions

Hiya, playing with a cheap mini sewing machine I was gifted. I haven't used a sewing machine since Home Ec 20 years ago.

First question is so basic that it isn't covered by any of the instructions I've read or watched. When I finish sewing a section, there are two threads hanging out of each end of the stitches. One is from my thread spool, the other from the bottom bobbin (according to my machine's instructions). If I pull the bottom thread, it just comes straight out. The top thread is at least looped around the bottom thread. Am I supposed to tie these together at each end every time? Is there some trick I'm missing?

Second question is maybe about my specific machine. The loops of top thread that go around the bottom thread are really loose. Any guess what I've done wrong to cause that?

Thanks in advance.