According to the USA IRS: You must claim all worldwide income on your tax return.
If your landlord is renting out the room and you just collect rent and pass it on to him/her, it is your landlord's income. Make sure any checks are made payable to the landlord or you can be responsible for the taxes (and any penalties that apply).
If you are renting rooms out (whether you own the property or not) then it is your income and you are supposed to claim it on your tax return - just as you would claim employment income.
This is self-employment Rental Income and claimed on Schedule E. You can deduct Rental Expenses (insurance, maintenance, etc.) on the same form.
If you run a business as sole proprietor you claim Rental Income & deduct Expenses on Schedule C.
Schedule E & C are filed with Form 1040.
If the entity is a Partnership of S Corporation, you claim Rental Income & deduct Expenses on Form 8825 & file it with Form 1065.
Be sure to consult a Tax Professional before filing any tax forms.