How install yii2 on FreeBSD

Please don't ask the same thing multiple times. Threads merged.
It also helps not to assume that we all know what you're talking about. For example, even though I'm pretty familiar with the way things work on FreeBSD I do most of my development using either Java or ASP.NET, therefor my expertise on PHP frameworks is quite limited. As such it would help to mention that yii2 is just that ;)

So I looked it up and noticed that it even has an installation guide. I'd follow that one.

As to FreeBSD: First thing you can do is search the Ports collection. For example like this:

root@feliner:/usr/ports # make search name=yii2
root@feliner:/usr/ports #
As you can see: no results. However, yii did give me something:

root@feliner:/usr/ports # make search name=yii
Port:   yii-1.1.17
Path:   /usr/ports/www/yii
Info:   High-performance component-based PHP framework
R-deps: freetype2-2.7.1 gettext-runtime- indexinfo-0.2.6 jpeg-turbo-1.5.1 kbproto-1.0.7 libICE-1.0.9_1,1 libSM-1.2.2_3,1 libX11-1.6.5,1 libXau-1.0.8_3 libXaw-1.0.13,2 libXdmcp-1.1.2 libXext-1.3.3_1,1 libXmu-1.1.2_3,1 libXp-1.0.3,1 libXpm-3.5.12 libXt-1.1.5,1 libltdl-2.4.6 libmcrypt-2.5.8_3 libpthread-stubs-0.3_6 libxcb-1.12 libxml2-2.9.4 pcre-8.40 pecl-memcache-3.0.8_1 php56-5.6.30 php56-dom-5.6.30 php56-gd-5.6.30 php56-mcrypt-5.6.30 php56-pdo-5.6.30 php56-session-5.6.30 php56-soap-5.6.30 php56-zlib-5.6.30 png-1.6.28 printproto-1.0.5 t1lib-5.1.2_4,1 xextproto-7.3.0 xproto-7.0.31
As such the best way to install this is using # cd /usr/ports/www/yii && make install clean, or maybe using a program such as Portmaster: # portmaster www/yii, this should also work.

But if you're looking for version 2 then I guess your only option at this time is to install things manually, you can follow my link to the installation guide.