Erm.... one person does one part of the week and another does the other. The pay is split according to the divide in hours (ie, don't have to do a 50:50 share). It depends on what the job is as to whether you can each have your own tasks or if you have to have some kind of hand over. It makes it easier for the employer if you happen to go together with someone else who happens to want to do the hours you don't, but there is absolutely no necessity to do this. There is no necessity to cover each other when the other is off, but again, in some jobs it's really helpful if you can. You have to work out how you split the week - doesn't have to be full days, one person could do mornings and the other afternoons.