Aluminum cable end tip crimp thingies, to prevent the cable from fraying and poking and scratching you. Pinch it on with side cutting pliers but don't squeeze too hard otherwise you'll cut all the way thru.

These crimps are for 1.2mm cables which is the standard size for all shifter derailleur cables.

Get a box of bigger 1.6mm



Secret tip: scoop up some grease with the open end so that it sticks to the cable and doesn't fall off or get catapulted across the room before you get to pinch it on.