I'm New To E-OS And I Want To Know That. Is There Any App Which I Can Use To Highly Compress Files in Elementary OS.
There are quite a few compression tools available, most commonly used are gzip, bzip2 & xz from command line or just use the Files GUI tool (right-click on a file and select compress).
You don't define what "highly" means, but most command-line tools have options to specify the compression level. Higher compression generally requires more memory (RAM) to work and can take a lot longer to complete both compress and decompress options.
Note that not all files compress well. Some may even become larger, it really depends on the content of the file, compression algorithm and level. Some algorithms will work better than others on different files, so there is no single "best" tool.
This all assumes you want lossless compression. Image, video and audio files are often compressed with "lossy" algorithms like JPEG, MP3, etc. These result in smaller files, but they do so by discarding some of the data. The higher the compression ratio the lower the quality of the decompressed image/frame/audio afterwards.