First time using dp needles - when I finished binding off - there is a space between the beginning and the end when I finished; in other words, not joined. Is this correct or did I do something wrong?
You probably did it right. When you knit in the round you are spiralling and not doing row on row, so the beginning and ends are a bit off in height one from another. When you work in the tail you can ususally fix that very smoothly with a stitch or two in the right places. You may have to experiment a bit with what works.
Yep, that’s perfectly normal - the end of a round is higher than the beginning. What I do is pick up a stitch in the first bound off st (not in the bindoff, in the center of it) and bind that off with the last one. It smoothes out the edge and can’t be seen.