... I have made
a mailing list on excel and now it is time to send out important
letters to customers and I need to put that mailing list on individual
mailing labels.

One way is to use MS-Word:
Tools Letters and mailings Mail Merge

This is a wizard with several steps
- Document type: labels
- Label options: choose standard label stock or use "new label"
- Select recipients: use an existing list (your Excel file)
- Arrange labels: use "address block" and click "update all labels"
- Preview labels: verify that you're getting what you want
- Complete the merge: Print

(I have Office 2003. I haven't tried label printing, but I use mail merge
for form letters.)