08 ford fiesta fitted a power steering pump today it’s the power steering pump that goes behind the engine but I tightened the power steering fluid pipe that connects with a nut but seems to be leaking still is there meant to be an oring I put in before I install the pipe 

I don't know about this case specifically, but yeah most probably. Fittings involving fluids like this do tend to require an o-ring to stop it leaking.

There'll probably be a groove of some kind for it to sit in.

There is definitely no grove on the end of the pipe anyway 

Oh, there is another type of connection that I forgot about last night. The following picture is an example of a flare type connection between two pieces of pipe. The two brass pieces slip over the two bits of pipe, then the ends are swished into a special shape, which are held tightly in contact with each other when the brass pieces are screwed together.

An alternative design involves pieces like in the following picture. The middle piece is called an "olive" and gets squished into place when screwed tightly together. If you ever undo it you may need to replace the olive to get a good fresh seal.

Perhaps it would help if you could provide some pictures of the actual fitting you're having trouble with.

On the pumps in front of the engine the pipes are single use and can't be refitted.  With those, the new nut must be fitted first.  Then the pipe is pushed through the nut.

I'm not sure if the rear mounted pump uses the same fitting or not.