To attach files to a discussion board posting, locate the Attachments section of the Create Thread or Reply windows, this is located directly below the area you would use to type your Message as seen below:

 

Choose Browse My Computer which will open up a new window which looks like the one below and allow you to navigate to the location on your computer that you have stored the file you wish to upload, click on that file and then click Open.

Once you have done so the window will close and return you to the Learn (Blackboard) window which appears as the one shown below. Once you have attached the file, click Submit. You will only be able to attach one file but simply repeat the process above to attach another file.