If you select a folder in the Finder, then select File menu-->Get Info, it will bring up an info window. Click on the flippy triangle next to "Ownership and Permissions" and set the permissions how you wish (you may need to click the lock to be able to do this). Then click on "Apply to enclosed items" to change permissions for every file in this folder as well.
I think this will only change one tier down; if you have more folders nested inside this one, you need to select them and repeat the process.