Rooting an Android phone is when you defeat the protection that keeps the user from having access to all parts of the phone’s operating system. If you do a search for your phone’s model number and root, you will most likely find several different methods to choose from and usually someone has posted step by step directions.
Once you have rooted your phone you can install apps that you can use to delete or disable any built in app just like if you tried one from the Google Play store and decided that you didn’t like it. The most popular app for doing this with a rooted phone is called Titanium Backup... as you might guess from the name it allows you to backup all of your apps, your operating system and has a multitude of other functions.
A custom ROM is an operating system that someone other than the manufacturer, or carrier has prepared for your phone. Depending on the type of phone that you have there could be many custom ROMs available. People prepare custom ROMs for a variety of purposes, most often for increased performance, but also for persons with concerns about their privacy especially with older phones.
Thanks for the explanation. Very helpful data.