Summarize:

Click or double-click the Chrome app icon, which resembles a red, yellow, green, and blue sphere. Go to https://www.youtube.com/ in Google Chrome. This opens the YouTube home page. Search for a video by entering its name into the search bar and pressing Enter, then click the video you want to download to open it. Click the video's address in the address bar at the top of the Chrome window, then press Ctrl+C (Windows) or Command+C (Mac) to copy it. Go to http://convert2mp3.net/en/index.php in Google Chrome. Despite its name, Convert2MP3 can download YouTube videos which aren't copyright-protected onto your computer. Convert2MP3 can download some videos in 1080p, though only if the video is available in 1080p resolution. It's near the top of the Convert2MP3 page. Press Ctrl+V (Windows) or Command+V (Mac) to do so. You should see the copied video address appear in the text box. This is to the right of the video's address. A drop-down menu will appear. It's in the drop-down menu. If you want to raise the video quality, click the "MP4 quality" drop-down box, then click a higher quality (e.g., 1080p) in the resulting drop-down menu. If your video's maximum quality is 720p, you can't select anything higher. This orange button is to the right of the "Insert video link" text box. Doing so allows Convert2MP3 to begin looking for your video. If you see an error that says "We are sorry. Converting music videos from YouTube is not possible in your territory / region" appear, your selected video has copyrighted audio (not necessarily music) that prevents it from being downloadable via Convert2MP3. It's a green button in the middle of the page. Your video will begin downloading onto your computer. Depending on your browser's settings, you may first have to select a save location or confirm the download before the video will actually download.
Open Google Chrome. Open YouTube. Select a video to download. Copy the video's address. Open Convert2MP3's website. Click the "Insert video link" text box. Paste in your copied video address. Click the mp3 box. Click mp4. Select a quality if necessary. Click convert. Click Download.