To be clear, the bar with icons at the top of the Mac screen is the Menu bar.
The Menu bar may have icons related to underlying System Settings panels or other utilities like BlueTooth and Wi-Fi. It may also have Data & Time info, User account. Some apps like malware scanners, printer drivers and such may also post an icon in the Menu bar.
If you click a Menu bar icon you will usually find some clue to what it is for. If you Option-click (⌥ click)a Menu bar icon you may find different clues, sometime for quitting the responsible app or removing the icon from the Menu bar. If you Command-click (⌘click) an icon you can drag it to a different position.
Guidance for using the Menu bar is here: What’s in the menu bar on Mac? - Apple Support
The row of application icons at the bottom of the screen is the Dock.
The Dock can be customized by following the guidance found here: Use the Dock on Mac - Apple Support
Re: the icon at the top right corner of you Mac: if you right-click it and select Get Info, what do you find as Kind?