new to this

[KaktoR]

Depends on how much you want to size down your games. Generally spoken: The stronger the compression, the more time will it take and also CPU/RAM resources, to be simple.

To get the "quick and easy way" you can use DiskSpan_GUI to compress your files.
You can also unpack your compressed archives with it too (Tools -> Unpacker).

In your example for "Sniper Elite 4" I guess you can just use srep+lolz if you want it strong, with cost of speed and pc resources, or srep+lzma with cost of compression ratio, but requires way less pc resources. But I didn't checked the game so I cannot tell you for sure.

Some games requires that you first unpack the files and then compress them. In most cases you use xtool to unpack the game files, but you should know what compression method the game is compressed with. For example "Sniper Elite 5" is compressed with zlib (if I remember well), so you have to use xtool first to unpack the files, then apply srep to get rid of duplicates, then use lolz or lzma to use final compression.

Maybe you have noticed the problem for "newbies" here. That's nothing to explain in a few sentences.