Hi Ansari.
I think you're on your way to find libraries. Good.
Background:
Typically, when a library is posted in the forum, it comes with the library files. For example: .jar and .xml files. These are built with a Java development tool. These go into the Additional Libraries folder on the development computer you have B4A installed, or if you have other drives available, the Additional Libraries folder can go there also.
But you only have one of these folders for each B4X development tool. It's up to you where you want those files stored.
The other type of library is the one you've found, with the file extension of .b4xlib.
These type of libraries are built with the development tool itself - for example: B4A.
They also go into the Additional Libraries folder, unless the author specifically states otherwise.
Use of The Library
If the library is available, so is an example app project together in the same post. This is how the author shows how the library is implemented.
Download the libraries to the folder mentioned above. Unzip the B4X project to another folder - wherever you like.
Open the project and run it in Debug mode. Follow along to see how it works. Place a debug stop in the code and step thru it.
You will see and learn from there.
Implementing into Your Project
That's where the "fun" begins.
Once you understand how the library works and all it's properties and methods, then you can move ahead with confidence and place it into your project.
Always know that you can come back to the forum for help. If it's a new library, posting to the original post is best, but most people think you should make a new post. If you do make a new post, its best to refer back to the original post with either a link or obviously the name of the library and post title.
Just some heads up on how to proceed.
Make it fun and the hours building B4X projects will go by fast.
All the best
Mark