Installing Memcached
Downloading
First of all, let's navigate to the download page. The link for it will vary depending on your operating system. Note that this guide expects you to be on Windows.

All of these files may seem daunting, but in reality, we only need memcached-1.6.8-win64-mingw.zip. Click on it to start the download.

Installing
Extract the zip, open the resulting folder, then open bin.
Next, click next to the current folder path and type cmd to open a Command Prompt in the current directory:
GIF from Dortania's OpenCore Install Guide

Run memcached -d
Memcached is now running!
You can close the cmd window.
Downloading the Memcache PHP extension
Navigate to here
All of these links may seem daunting, but in reality, we only need the 5.3 Thread Safe (TS) x86 version. Click on it to start the download.

Installing the Memcache PHP extension
Extract the zip then copy php_memcache.dll to C:\XAMPP\PHP\EXT\
Add this under [PECL] in C:\XAMPP\PHP\php.ini:
extension=php_memcache.dll
Your php.ini's [PECL] section should now look like this:
[PECL]
;extension=php_ming.dll
;extension=php_pdo_oci.dll
;extension=php_pdo_oci8.dll
extension=php_memcache.dll