Here are the simple steps to create a GitHub Tag, when you release build from master.
Open source_tree tab
Right click on Tag sections from Tag which appear on left navigation section
Click on New Tag()
Click on Add Tag from give name to tag (preferred version name of the code)
If you want to push the TAG on remote, while creating the TAG ref: step 5 which gives checkbox push TAG to origin check it and pushed tag appears on remote repository
In case while creating the TAG if you have forgotten to check the box Push to origin, you can do it later by right-clicking on the created TAG, click on Push to origin.