The Desktop Application Skype for Business opens every time you sign on in order to make it easier to communicate with colleagues. It also makes it so in Outlook and ALL other Microsoft Apps you can see whether a person is available, giving a presentation (powerpoint or video) and more!. Of course, you can just close the window, but it will remain on in the background so others can message you during the day or call you and share content. If you would like to turn this auto-run feature it is pretty easy but you are encouraged to open it on your own regularly as it WILL be a helpful tool for you all day!
From the Skype window, select the "cog" in the upper right hand corner (not the down arrow.)
Click on the "Personal" choice in the left-hand column.
"Un-check" the option to "Automatically start the app when i log into Windows" and then Click "OK" to save. You're done!