I wish to use music as background on my videos.
You really, really need to learn the business. Most music is copyrighted, and you don't want to use copyrighted music.
Every program you use has a tools menu. If you use tools a lot it will be a toolbar across the top of the screen. If you rarely use tools it might be hidden. In Windows you can click "Start" and select "Control Panel" and that gives you a menu of menus to control everything the computer does. You can right click anything and most of the time get a menu for that specific item. For example if you right click the desktop you have the option to rotate the monitor image in some graphic cards. That allows you to have an image that is high instead of wide, by turning your monitor. You don't need to memorize all these things, just be aware that they are in there. Then you can claim to know how to operate a computer at the beginner level.
Browsers have optional addons, and you can find that in the menu somewhere. Click "Get More Addons" and search for "download" or whatever interests you. If that doesn't work for you then you can go to download.com or tucows.com and search for a standalone program.