Navigate to http://portal.office.com and sign in with your credentials.
After signing in, press the OneDrive button to access your files.
Right click the folder or files you wish to share, press Share.
Click the box, pictured below, to change the permissions for that selection and choose the appropriate one.
Add whichever users need access to the file and press Apply. It will show a summary of the users you have added and ask if you would like to continue. Press Send and those listed will receive an email invitation to access the files you wish to share.