Want to Tag my mp3 song names without the song number

To Whomever it may concern:

I have a lot of music with filenames such as 01 Better than Ezra - In the Blood.mp3,
or this is how they show up in the explorer window.

I would like to use this program to have all of my songs simply have the: Artist - song name,
such as: Better than Ezra - In the Blood.mp3, don't want song number or album, just that format.

Lastly I have underlines instead of spaces in filenames or song names, for ex: the_all-american_rejects-swing_swing-its
if you could help me with this too that would be awesome.

I am using this software for the first time so you may have to walk me through it like a rookie.
If you could figure this out for me it would be a life saver. Thanks in advance!

Press F1 and you will find the user manual that explains how to use MP3Tag.

But what you are looking for is

Convert -> Tag to Filename, set whatever naming pattern you prefer, press [OK]

Keyboard shortcut is Alt+1

If you really want to fiddle about with the filenames only then you could create an action of the type "Replace with regular expression" for _filename.
Enter this as search string:
^\d\d
leave a space at the end after the last \d.
The "\d" means "any digit"
Leave the replace string empty.

The better way would be to fill the tags first and then create filename out of them.
As Chris Hirst said: use the function Convert>Filename - Tag.
I would suggest this pattern:
%artist% - %title%
This will put (unfortunately) "01 Better than Ezra" into artist as there is no unique separator between the number and the artist - but it may be easier to deal with such stuff if it is already in a tag field.

The other problem with the underscore:
Create an action of the type "Replace" for _FILENAME
Enter as search string: _
Enter as replace string:
(this time a space character - does not show up here :unsure: )

If you are not sure how to create an action, see the FAQs /t/967/1