When you are working in Office 365 you have the choice of storing your documents between two places, OneDrive for Business or a SharePoint site.
It’s so easy to save all your documents to OneDrive for Business because the link to your OneDrive for Business is always accessible at the top of the page. This is ok if the document is for your sole use however, if the document requires to be shared amongst a team, then saving it to a SharePoint site would be the recommended way to go.
Files in both OneDrive for Business and a SharePoint team site are stored in the cloud and can be synched offline to your computer.
OneDrive is basically an online version of your “my documents” folder so for storing personal documents you don’t wish to share; perhaps a draft document that you wish to retain control over before it moves onto a project site within SharePoint or if you plan to share files individually with a limited lifecycle (for example, a photographer might use one drive to share photos with a client).
Be aware though you cannot create metadata or create any kind of workflow within OneDrive.
SharePoint is used when you are working as part of a team or an organisation. Documentation & permissions are shared & owned across several individuals. Permissions are granted on a site basis rather than an individual document level. Lists and libraries are available to store content as well as the ability to put in place metadata, custom views to help find documentation, versioning and workflow. Sometimes a document may originate in a personal document area and later moved to a SharePoint site when more people are required to work on it.