The simplest method of addressing envelopes is to use a word processing application such as Microsoft Word.
If you do not have Word then I would recommend downloading and installing a copy of Kingsoft Office Suite Free 2012
which is compatible with the latest versions of Microsoft Office documents and is free for home users.
Once the application is installed, open Kingsoft Writer 2012 (which is very similar to Microsoft Word).
Click on File then on Page Setup and select the Paper page tab where you can then choose the Paper size to use for your envelopes.
In the Paper size drop down selection listing, choose an envelope size such as C6 Env.
If you are unsure which option to choose, then simply measure the size of the envelopes you are wanting to print on and set the Width and Height values (in centimetres) to match that size.
Next switch back to the Margins page and select the Orientation that you want to use for your envelopes, i.e. Landscape or Portrait.
On this same page you can also increase the Margins to position your address text more centrally on the envelope.
Click on OK to exit Page Setup.
Type your address on the main Kingsoft Writer page and you are ready to print the envelope on your printer.
Kingsoft Writer can also use Mail Merge to write a series of addresses on a stack of envelopes if you need to write a number of addresses.
Simply create a list of your addresses in the Kingsoft Spreadsheets application, putting each 'address field' in a separate 'box' in the new spreadsheet so that you have a column each of 'Names', 'Address line 1', Address line 2, Town, County, Post code etc.
Then in Writer, click on Tools, Mail Merge toolbar, then in the toolbar, click on the left icon to Select Data Source and select your addresses spreadsheet document.
Next, click on the icon for Insert Merge Field and select all the address fields to insert into your new Envelope document.
Finally, adjust the layout of the fields by moving fields on to new lines as needed. You can also change the font and character size of the new address fields to make the text larger or bolder etc.
Last of all, click on the icon for View Merged Data which will show you what your addresses will look like when printed on the envelopes - you can step through the list of addresses using the controls in the toolbar.