I would like to add some MP3 files from my computer to Google music. Music Manager doesn't seem to let you select specific files to add. Additionally, I don't really like Music Manager to say the least. Is it possible to upload files from my computer without Music Manager?
If it's not already visible, open the menu by clicking the hamburger menu.
Scroll to the bottom of the menu.
Click "Upload music". You'll get a dialog box. You can either drag-and-drop music files onto that box (assuming a modern enough browser1) or you can click "Select from your computer" to get a more traditional file select dialog.
1 I use Google Chrome. These screen shots are from version 47.0.2526.106 m.
Perhaps this Chrome extension will help you.
Upload files to your Google Music account without installing the Google Music manager.