USB-C (using the USB 3.1 protocol) to HDMI 1.4, USB 3.0 (downwards compatible to USB 2.0) and USB-C (Power Delivery) adapter for connecting and transfering audio/video signal, data and power from the MacBook 12″ with USB-C port.
The HDMI port supports HDMI 1.4 and resolutions up to 1080p and even UHD 4K to be displayed on an external display, projector or TV while transfering the audio signal in digital multi-channel quality. Through USB 3.0, data can be transferred at up to 5 Gbps. The USB-C port allows to supply the connected devices such as an external USB HDD with power while charging the MacBook 12″ at the same time (Power Delivery).
Important Notice: Unplugging the power delivery (PD) from an external power adapter via the LMP USB-C Multiport Adapter can cause the sudden interruption of the power supplied to attached devices (i.e. an external USB HDD). This in return causes attached devices to be unmounted or to loose the connection shortly (the connection is re-established automatically after 2-3 seconds) which may bring about a loss of unsaved data. Therefore, we strongly advise to save all data and/or unmount any attached device before unplugging the PD!
Note: Not compatible with Apple USB SuperDrive
Basically, you can use only iMac (27-inch, Late 2009) and iMac (27-inch, Mid 2010) with a Mini-DisplayPort connection with current Mac with Thunderbolt 3 (USB-C) ports. You need a USB-C to Mini-DisplayPort adapter (e.g. 16134/16138, LMP USB-C to Mini-DisplayPort adapter) or a USB-C dock with Mini-DisplayPort port (e.g. 18641/18645/19009, LMP USB-C Travel Dock 4K 9 Port or 17113/17278/18954, LMP USB-C Compact Dock 4K 8 Port or 17116, LMP USB-C Display Dock 4K 10 Port). Then a Mini-DisplayPort to Mini-DisplayPort cable (8305, LMP Mini-DisplayPort to Mini-DisplayPort cable) must be attached to the dock and the iMac.
With iMac (Mid 2011 to Mid 2014), it is possible to use the iMac as monitor with a Thunderbolt connection only. With newer iMac, a Target Mode with an iMac is not possible anymore.
For further details, see https://support.apple.com/hr-hr/HT204592