I have this couples walk but the person on the follow seat is just sitting being carried around, why?

Make sure that the person on the follow seat does not have any scripted attachments on that are interfering with it. These can sometimes be things you would not expect which have had odd scripts put inside.

Also check that the follow seat still has the scripts etc inside it, and that they have not been accidentally removed.

If it does have all scripts inside and you are sure it is not caused by attachments the other person is wearing (i recommend they take ALL attachments off to test this), then try resetting the scripts and restarting them using the following procedure.

a. Drop the walk on the ground right click on it and select edit
b. Go to the tools menu at the top of the screen and select the option 'set scripts to running in selection'
c. Then go to the tools menu at the top of the screen and select the option 'reset scripts in selection'

This should fix any scripts which may have stopped running or working for any reason.

When I sit on the Walk I end up somewhere else, it will not allow me to sit on it.

On a few occasions ive had reports of this problem. It is related to certain scripts in attachments that move your avatar about. Typical scripts which might cause this to happen include shields scripts which try to lock you in position, or collars which make you follow someone. Try detatching any of these attachments if you have them on, and are experiencing the above problem.

I attached the walk but no ne else can select it to follow

The walks are not attachments, they are essentially vehicles. You need to drop them on the ground and sit on them to use them. Each person sits on there respective sections.

When I sit on it, my legs move but the actual walk stays fixed in position and wont move

This is usually down to the estate owner haveing physics disabled in there estate tools. Sometimes this is done in an effort to reduce lag. The tools are however only ment to be used temporarily to help resolve a problem. You could ask the estate owner if they intend for this to be turned off as it will basically stop any vehicles from functioning correctly on there sim. If you think this might be the problem and are not sure, try using the walk somewhere else, perhaps on mainland where you know that physics will not have been disabled.