This video in the "Who Sees What" series describes how to open up access to records, if you have set the default sharing settings to anything more restrictive than Public Read/Write. You can use Sharing Rules to extend access to users in roles, public groups, or territories.
Find the entire series in the Lightning Experience at sforce.co/whoseeswhatlightning.
To view the Classic UI, follow this link: sforce.co/whoseeswhat. Please share and leave a comment!