what different in SDK13 between ble_nus.c and ble_nus_c.c ?

[Mikhail]

I need use NUS services (UART over BLE) What file and functions should I use?

[endnode]

That depends on what "side" of GATT link are you looking for;) BLE is asymmetric on pretty much every layer and NUS need GATT Client and GATT Server. ble_nus is GAP Peripheral + GATT Server (usual "embedded" option, that's why it is kind of "default"), ble_nus_c is GAP Central + GATT Client option (usually handled by device with higher power budget = bigger battery).

[endnode]

Well if you are GAP Central then you use GATT Client, no characteristics to add, all the functionality should be in the example already.