To cut the thread and finish you should end the row with chain stitch. Then cut thread 2 to 3 cm long from the needle, that is, the last chain stitch.
Remove the needle by pulling and then adjust the knot so that it formed. Finally, with a much smaller crochet needle, yarn excess is introduced between the stitches from the back. Thus it remains neat and presentable good tissue for attaching it to where appropriate.