How to Limit WP Plugin to Work where it is needed

I have a script which I wanted to insert into my WP site but I couldn’t get it to work except I upload it to my file manager! So j tried converting the script to a plugin. I succeeded in making it appear as a plugin in my WordPress dashboard but the plugin automatically shows all over my site including my backend and frontend (which makes my site very slow and scattered, and my site Automatically took the plugin appearance). Meanwhile, I wanted the plugin to remain functionless until I generate a shortcode for it, then it can function wherever the shortcode is inserted.

Unfortunately, I am totally new to WP plugin creation, in fact, I have never created one before! So I just uploaded my script file which contains css, js, and php into the WP plugin directory. So my codes are exactly the way they are in my program. The only thing I did was to add the WP plugin line of code to make it show as a WP plugin.

Please can I get a help on what to do from anyone here on this? Thanks in advance for your help!