The templates to design Avery 11136 can be located at
https://www.avery.com/templates/11136
Use the red Start Designing button to use Avery Design & Print Online. If you choose a pre-designed template, the text will be automatically centered on the inserts and you can just click Edit One in the top right and change the text. If you place the text for the front of your first insert at the top left, then the back for that insert right next to it, you can leave the connecting perforation in place and easily fold to insert.
If you prefer to use Word, the downloadable Word template is lower on the same page as Design & Print Online. Or you can open the built-in template in the Mailings tab by clicking Labels, then Options, Avery US Letter as the Label vendor and choosing Product Number 11136 and New Label.
To format the built-in template, either use Ctrl + A on your keyboard to select the entire table, or click on the 4-arrow icon at the top left of the table. On the Table Tools tab, choose Layout and click the icon to Align Center. 
These inserts are not a standard size sheet, so see our Tips for Printing Worksaver Tabs 11136 and 11137 or contact us for more help.