To be able to use the addresses in a mail merge operation in Word, the format of your address list in Excel should have one row per address with each element of the address in its own cell. A proper setup would be like this:
A1 Name, B1 Street, C1, Apt., D1 City, E1 State, F1 Zip_Code.

The way you have the addresses laid out now seems to be the most logical but it is the most difficult to work with.

If this is a Word Mail Merge situation, the easiest way is to enter the Mail Merge area of Word and you should see a prompt to either create a "source" document or to locate the source document. Choose to create the source document and you will be prompted with the proper headings and then all you do is fill in the data.

If you already have an extensive list of addresses in Excel, it may pay you to re-format the data to be acceptable for a mail merge.