Export this file to a PDF: File > Export… Choose PDF
But ask on the first place, how they need it: Color Mode and Color Space, minimum resolution, PDF standard like X-1a or X-3 or X-4, etc. It could be very different with each printer and such huge players as Walgreen’s might use different machines on different places.
If you want to print a photo (like the FUJI photo printer they use on some places), you might want to export it as JPG with sRGB output colorspace. Better for quality would always be a PDF, if accepted.