What is library to do that (build *.min.js file like jquery,
owlcarousel)
I recommend using UglifyJS. You can do many process with this module and minification is one of them. Here are other online tools that might as well help you. Javascript-Minifier and Minifier.org.
What heppend after build? Seem *.min.js file was minify and obfuscation?
Minification and Obfuscation are different process with different intention. Minification just removes unneeded spaces and changes some variables to make it shorter and a little bit harder to understand. Whereas, obfuscation intends to make the script unreadable by human. Therefore, if you want to know if the build process of a library make your code minified and obfuscated, it really depends on the library you use. Most of them will do only one thing either minification or obfuscation.
*.min.js file will not deobfuscate ?
Yes. Minification will not deobfuscate your code.
And here is an online Javascript obfuscator in case you need one.