Howdy and welcome Norman.
You'll soon discover the tagging and entry capabilities to be pretty extraordinary.
To accomplish what you had to do the hard way, with one or more tracks selected, do any of the following:
1. Open the Action Window > Tag and click-to-edit a value there for a given field, such as Genre.
2. Press F2 (or right-click Rename - F2) and edit a value directly in the file list (or panes). If you are not in the column you want, use Tab or Shift-Tab to move right or left, until you're editting the desired cell. Enter the new value, and hit Enter.
3. A faster way to edit a given cell's value for a group of files: Select the first file, and then Shift-Select the last file in the range but be sure to click within the cell you want to edit. This sets that cell as the target. Use F2 or right-click or Rename to edit.
There are other ways, such as drag-n-drop, tagging mode, but we'll leave that for now.
An immediate Undo will always help you out, so you can try some things...