Locate a micro SD card I installed in my Galaxy tab S 10.5? Answered

I assume you mean in the file structure, not physically. (If you do mean physically then immediately have someone take you to a doctor, you've probably suffered a bad concussion.)
Using a file manager app like Astro or ES navigate to the root of the file structure (not the root folder). There you should see a folder named "storage". In it there should be a folder named "ExternalSD" or "SDCardExternal" or some other variant. If not you may have to go to Settings...Storage... and select "Mount SD Card".
Your best bet is going to be googling it to find an answer from someone who owns the actual device you're using.

IF you download ES file manager from google aps store you should be able to find it, transfer files and apps to it easily.

Note that in general your android system will not automatically see the memory extention as part of the main memory, consider it more like a hard drive you have to put things into.

Usually it is right where you inserted it, for the rest check Google in regards to SD access restrictions in Android.