[YotaPhone] Amplificator:
I've never used a Mac before so you are probably better off looking here: http://xdaforums.com/showthread.php?t=1917237

..or doing a google search if that link is not enough for whatever version of OSX you are using.

CyanogenMod does a good job of giving a quick explanation of what fastboot is: https://wiki.cyanogenmod.org/w/Doc:_fastboot_intro

But basically no matter how much you bricked your device you can always just boot into this mode and re-flash a working rom, so take note in the Settings -> About Phone what region your rom is.

The rom I'm currently using has a build number of: LRX21M.5.0.0-RU1.1.134 <-- RU is the important part, because knowing this you can always revert back to that rom if you brick anything. Here's the link for the Yota Devices ftp server with roms for all regions: ftp://fw.ydevices.com/YotaPhone2/Firmwares/

You can access fastboot using either volume up + power button or volume down + power button, I've forgotten which :)

Fastboot is always used to flash new recoveries for example, just like TWRP for our YotaPhone 2:

http://xdaforums.com/yotaphone-one/development/twrp-3-0-2-0-yotaphone-2-t3494023

http://xdaforums.com/yotaphone-one/development/twrp-twrp-2-8-5-0-recovery-yotaphone2-t3142024

When you download a rom from Yota Devices as a .zip file it contains a bunch of files that are more or less images of partitions.. So what you do when flashing is essentially just restoring the rom image to the System partition and all the others.

What I imagine people are having problems with when flashing cross-region roms is that they install the baseband from a region which their device doesn't fully support, which could indeed result in issues. Yota Flasher will very likely do this, as this is a simple tool that just downloads whatever rom is the latest for the region you pick and then it flashes it. It does not take cross-flashing of various basebands into account.

What you can do then is to just install the baseband that is actually meant for your device after using the Yota Flasher, or if you manually flash all .img files from a zip, just simply not flash the new baseband.

The latest RU rom for example, on the Yota Devices ftp server, is version 124, which will OTA update to 134 once installed.

Link for the RU rom is here: ftp://fw.ydevices.com/YotaPhone2/Firmwares/RU/5.0.0-RU1.1.124.zip

Inside this zip file are these files:

Archive: 5.0.0-RU1.1.124.zip
inflating: 5.0.0-RU1.1.124/emmc_appsboot.mbn
inflating: 5.0.0-RU1.1.124/userdata.img
inflating: 5.0.0-RU1.1.124/recovery.img
inflating: 5.0.0-RU1.1.124/boot.img
inflating: 5.0.0-RU1.1.124/system.map
inflating: 5.0.0-RU1.1.124/system.img
inflating: 5.0.0-RU1.1.124/cache.img
inflating: 5.0.0-RU1.1.124/radio/rpm.mbn
inflating: 5.0.0-RU1.1.124/radio/sbl1.mbn
inflating: 5.0.0-RU1.1.124/radio/tz.mbn
inflating: 5.0.0-RU1.1.124/radio/NON-HLOS.bin

So what you would do is essentially just flash the relevant parts and not flash the irrelevant parts, such as radio if you have a different devices with other bands.

VirtuaLeech gives an example in another thread on using fastboot: http://xdaforums.com/showpost.php?p=69461892&postcount=76 with the -S flag which splits the transfer due to size limitations.

It can all probably sound really technical if you are new to this, so I strongly suggest you flash using Yota Flasher first, then read up on fastboot if you want :)

It does take a bit of reading, but using fastboot you can always restore your device to any rom you want, no matter if you brick it trying out new stuff.

The worst that could happen is that you will lose the data currently on the phone so you'll have to set it up from scratch, but at least fastboot will ensure that you can always reflash to a working rom.

This goes for more or less every device out there. Fastboot is a tool from Google, so it's pretty generic stuff :)