Maybe a general explanation is needed.
“Professional” Mikrotik devices come with no configuration at all.
“Soho” Mikrotik devices come with a default configuration (the relative settings are usually commented as “defconf”)
This default configuration is (slightly) different on each device as it usually reflects what is the “intended” use of the device.
Typically the lower numbered interface (ether1) is self-standing and it is WAN, all the other interfaces are put together in a bridge that is LAN.
In the case of your LTE devices, the LTE modem/interface is WAN and all other interfaces are put together in a bridge that is LAN.
Potentially each and every interface on Mikrotik devices can be added or removed to/from a bridge and be categorized as either WAN or LAN.
Device configuration can be managed by:
- browser (Webfig)
- Winbox (Mikrotik proprietary tool) that can connect BOTH to the IP of the device and through a special protocol to its MAC address (i.e. even if the device has no IP on any port)
- SSH, telnet, etc.
The “best” tool (IMHO) is Winbox (there are two versions of it, the “old” 3.x version (that is simple and clear, but runs only on windows or under WIne) and the 4.x version, which is new, experimental, cool, dandy, has dark mode, runs on almost anything but is almost as unreadable/unusable as webfig (which can sometimes be confusing).
Besides, WInbox allows you to (size of your screen permitting) open multiple windows so that you can see the effects of a changed setting in another section of the config.
Inside both Webfig and Winbox there is the terminal, a CLI that is usually much more powerful that the GUI, but some tasks are much easier to do in the GUI.
The three commands holvoeth just posted, as an example, are only a few clicks/choices in drop down lists, but you can copy and paste them in terminal as they are, which is even more handy.
When you open terminal, if you press F1 you get the general help (and useful hotkeys), when you are typing commands, there is an extremely handy [TAB] autocompletion.
The initial impression on the above (before and besides the complexities of the configuration settings) may be outputting, but after a little bit of playing with the Winbox and Terminal you will find how everything (or almost everything) is quite logically organized and the CLI is not that much different from the command line of WIndows or of Linux, each section of the configuration is essentially a path/folder/directory, i.e. a one liner like:
/interface bridge port remove [ find default-name=ether1 ]
can be executed also as:
/interface bridge port ← change to the appropriate path
remove [ find default-name=ether1 ] ← run the command there
the prompt always shows the current directory you are in.
Some (hopefully useful AND shameless plug 
) references (things to do or not to do for beginners), once you have got the hang of the GUI and CLI interfaces:
http://forum.mikrotik.com/t/the-twelve-rules-of-mikrotik-club/182164/1
http://forum.mikrotik.com/t/gp-csa-for-mikrotik-devices/182176/1