It depends on what device you are using to share. 

  • Laptop/Desktop: If you are currently working on a document, in the upper right hand corner is a share button. By clicking on it you will have the option to share via an email address. If you have not saved the document in OneDrive, it will ask you to do that first. Or Navigate to where you have the file saved in your OneDrive folder, right click and select the Share that has the OneDrive cloud icon. Then you will be able to enter the email address of the person you wish to share the file with. 
  • Tablet/Mobile Device: If you are currently working on a document, in the upper right hand corner is a share button. By clicking on it you will have the option to share via an email address. If you have not saved the document in OneDrive, it will ask you to do that first. Or Navigate to where you have the file saved in your OneDrive app. Select the three periods to bring up more options (...) and select share. Then you will be able to enter the email address of the person you wish to share the file with.
Video: Check out this short video from Microsoft about Sharing in OneDrive