The terms of your lease will state whether you are allowed to sub-let, and what conditions there are. These can include restrictions on whether you can sub-let part of the premises, or can only sub-let the premises in their entirety, or restrictions on what rent you can charge.
Bear in mind that when you sub-let, the original lease remains in force (and you have a separate sub-lease with the tenant); you retain your liabilities under the original lease. The terms of the sub-lease will be limited by your lease - you cannot, for example, grant a sub-lease which is longer than your own lease - and the landlord may have the right to approve the terms of the sub-lease before consenting to it.
