When the lower floor is made of concrete you will need a special fastener to attach the wood to it unless one has already been embedded for this purpose.
Attaching deck stairs to concrete pad.
The fine homebuilding article stronger smarter deck stairs by steven baczek and mike brussard issue 258 april may 2016 offered a number of great suggestions.
However if you are landing on the yard you may want to install paver blocks or fill the area with compacted gravel to promote drainage.
Attach the 2x6 board to concrete pad with masonry anchors.
If you attach the bottom end of your stringers directly to the concrete footing pad that long stretch of open wood grain will absorb water and rot even with.
In order for a wooden stairway to be safe the stringers support boards should be securely fastened to both the upper and lower floors.
The hangers are fitted to the back edge of the stringer and then bent to contour to the bottom edge.
If the stairs are resting on a concrete slab or a patio then the slab or patio should also be built with a similar foundation to resist frost movement.
One of the easiest ways to attach deck stair footings to concrete is through the base plate.
Attaching deck stairs to footings.
These hangers are adjustable to fit most types of wood structured stairs.
Guertin also explains how he pours a concrete stair landing pad and how he attaches the bottom of the stairs to that.
If no concrete pier is used the post should bear on the footing and stringers should bear on 2x4 blocking fastened to 4x4 posts with 8x3 1 2 screws or 16d nails.
Each tread is made of two lengths of 2x6 board.
When building a landing for deck stairs typical codes require the pad to extend beyond the steps about 36 inches behind the steps about 12 inches and on the sides of the steps about 6 inches.
If you re installing two different colors of boards for your deck then you can screw the accent color boards into place temporarily to act as guides for the primary color boards.
Place the board between the stringers and attach to stringers with 3 galvanized deck screws.
As a bonus he details a rock solid method of attaching the bottom railing posts to the stairs.
A typical pad has a 4 inch layer of gravel underneath and about 4 inches of concrete on top.
Concrete slab or patio landings.
Several building manufacturers make hangers that you can use to fasten stair stringers to concrete.
A concrete pad does not require the footings to rise above grade like other landing types.
Stair stringers should always land on a level and well drained surface.
Determine what type of landing you are going to have.
On the decks i built in the past i never gave much thought to how secure the connection was between the stairs and the deck frame.
If you are landing on a concrete pad or a patio this should not be a problem.