how to install Photoshop CS2 on (Mac OSX) Yosemite 10.10.2

Thank you for your response,

so I can't do anything with it?

‌CS2 will not install or run on modern Macs with Intel chips running OS X 10.10 (Yosemite).

CS2 is an old PowerPC application written for older Macs with PowerPC chips (incompatible with Intel chips) running OS X up to 10.3.8.

Modern Macs (all have Intel processors) running OS X with Rosetta (which enables Intel chips to run PowerPC software) will run CS2 but Rosetta was discontinued by Apple in OS X 10.7.

I cannot say whether the software will install/work on the OS you ask about, but in any case you need to get a special version of CS2...

Error: Activation Server Unavailable | CS2, Acrobat 7, Audition 3 -

http://helpx.adobe.com/x-productkb/policy-pricing/creative-suite-2-activation-end-life.html