Where do I store my files such that they can be found? I'm trying to install an app from an apk file, and I've moved it to my phone via USB; however, I cannot locate it.  What would be an easy location to which I could move the apk file such that it would be simple to find via a file browser?
This is what I'm looking at in USB on my PC.

I search for the directories shown in my file browsers, like acct, cache, config, d, data, dev, etc, mnt, proc, ...  None of these can be found on my PC.  I search for the PC directories on the phone, and I can't find them.  So, where can I find an overlapping directory?
I'm on 4.2.1 HM2013002 (China Unicom).  China Mobile MIMU, model 2013022.
Alternatively, as a workaround, might somebody be able to post an Android Enthusiast-local tutorial describing how to remotely install an app?
First a description. The path that contains acct, cache, config, d, data, dev, mnt, proc, etc is the device's root directory. The root directory is the root of all filesystem hierarchy in an Android device.

When you connect an Android device via USB to a computer, usually via MTP in newer devices or USB Mass Storage in older devices, the root directory of Android is never exposed to the computer. But rather only a small number of directories are exposed to the computer. The directories that are exposed to computer connected to USB is the external storage. 

The path to the external storage, unfortunately, varies by device. The external storage of many Android devices points to the SD Card storage; this is not necessarily always the case, such as with devices that doesn't have SD Card, the external storage actually points to a regular folder. These are some of the locations that external storage may be in:

/mnt/extSdCard/
/mnt/external_sd
/mnt/sdcard/
/storage/emulated/0/


Many Android file browser application generally have at least two specially programmed location to open, one showing the device root and the other the external storage. Look if your file browser application shows the external storage. If your file manager don't show you your external storage by default, try downloading OI File Manager, this file manager shows your external storage by default.

Once you saved your apk there, you should be able to just tap on the APK to install it in most file manager worth its salt.