Question: how to connect a logitech k400 keyboard?
Answer: Connect.
Step 1: Insert the Unifying receiver into a USB port on your computer.
Step 2: Pull to remove the yellow battery tab.
Logitech Options. K400 Plus is a plug and play keyboard loaded with features right out of the box. ... 
Logitech Unifying wireless technology. ... 
Replace batteries.
Customer Support.