how to save mailing addresses so I don't have to type it on envelope everytime

You could create a mail merge, but if you send to the same list every month, it might be just as efficient to create a file of addressed envelopes. Start with Mailings | Create | Envelopes. Set up your envelope and click Add to Document. See http://WordFAQs.mvps.org/DetachEnvelope.htm for instructions to detach the "letter" page from the envelope so that you're left with a single envelope. After the delivery address, press Ctrl+Enter to start a new page. Use the Envelope Return style for the return address and the Envelope Address style for the delivery address. Repeat as needed for all the envelopes, then save the file.

If you have a varying subset of the same list, then a mail merge will be more appropriate. On the Mailings tab, in the Start Mail Merge group, click Start Mail Merge and choose Step by Step Mail Merge Wizard. This will step you through creating a data source that contains all the addresses and then selecting the addresses you want for a given mailing and merging them to an envelope mail merge main document that you create.

If your Office version includes Outlook, store your contact addresses there. Word can use them individually or via mail merge (or with http://www.gmayor.com/Envelope_Label_Add_In.htm ) 

If not, then for Christmas card etc lists I would create an Excel worksheet or a Word table as a data source for mail merge. See http://www.gmayor.com/convert_labels_into_mail_merge.htm   for the format.