Normalizing Mp3 Songs...

If you are just looking for the folder where iTunes stores the song, right-click on the song in iTunes, then choose Show in Finder (second last option). You need an application to change the volume of the song outside of iTunes. You cannot do this from the finder.

By folder, do you mean album or playlist?

iTunes can be set to normalize all your songs automatically. This option is in iTunes > Preferences > Playback > Sound Check. Sometimes the results aren't great, so you can adjust the volume on songs individually:

• If you search for one of the songs (search box in top right corner of the iTunes window), you'll see a list of search results.
• Right-click on the desired song to get the contextual menu (or click on the three dots that appear on the right if you hover over the song).
• In the contextual menu, in the bottom third, there will be options to Show Album, or Show in Playlist. Select the appropriate one.
• Select all the songs in the album or playlist you want to change. Command-click lets you toggle a song's selection. If it is an album and you want to change all the songs in it, right-click on the album name, then select Album Info.
• Command-I or menu item Edit > Song Info will bring up an info pane for your selection. You may have to say ok to editing multiple items at once.
• In the Options pane, you can change the volume adjust amount.
• Click OK to commit the adjustment, or Cancel to keep the original value.