Machine not sewing. Even though I think I have threaded machine correctly it does not sew fabric

Question

Even though I think I have threaded machine correctly it does not sew fabric together. Just cuts fabric off but does not sew it!Help needed pls! I think I've threaded by overlocker right (Riccar RL 913) but the stitching aint right, threads not weaving together, Needle is stitching on top but no back stitches while the lower & upper loops just trail along. What I am doing wrong?