This is a house where residents have their own bedsits, but share some facilities, normally the kitchen and bathroom. A change of use from an ordinary dwelling to an HMO with up to six residents does not require planning permission. If there will be more than six residents, planning permission would be required. In some circumstances such applications can be problematic it is advisable to discuss your proposals with your Planning Department before getting any plans prepared.
Some Local Planning Authorities have removed the rights for change of use from an ordinary dwelling to an HMO by issuing an Article 4 Direction. If your Local Planning Authority has issued an Article 4 Direction you would need to apply for planning permission for a change of use even if there are no more than six residents. Your Planning Department should be able to advise if this applies to your area.