Question
I have an orchid that has grown a new plant on an old flower seem can I pot this and how would I do this please

Answer
Jackie, this is called a keiki.  Yes, it can be potted up after separation from the old flower spike.  Favorable results are best when you wait until the keiki has roots at least  5 cm in length.  Then you can separate it by grasping it near its junction with the old flower spike and twist it until it separates from the old flower stem.

Choose a pot size just large enough for the keiki's roots. and pour some of the old potting mix from the mother plant into the pot sfter inserting the keiki's roots.  Avoid both the extremes from too dry to too wet when you water.  Avoid direct sunlight.