What the property/building is used for doesn't matter. You own it, and someone else pays you so that someone else can use it. What they pay you is rent, any way you look at it. The income gets reported on SCH E as a part of your personal tax return.
You "WILL" have more questions if you've never dealt with rental property before. Feel free to ask them here. While I already know what a majority of your questions will be, I'll wait for you to ask them. Otherwise, the "information overload" all in one shot has the tendency to overwhelm a first time landlord.
What about the property taxes? Is that building or floor space included on your property tax bill, and is it a part of the designated "heated/cooled" space you are taxed on by your county? (What state by the way?)
Depending, you "might" be reporting that you rent out a part of your primary residence, and that will affect your depreciation amount, deductible rental expenses, and the such. Or do you already know how to deal with that maybe?
If purchased on the same closing statement as your primary residence, then you'll have to allocate both land and structure values to the building and the property it sits on. But that shouldn't be a big deal to do anyway.