By default, any template (or section, or line item, or content block) you create in your library will be "Private" by default - Meaning only you will see it and not your team members.
Sharing Individual Items
When you wish to make any library content visible to other team members to allow them to utilize the template (Or section, line item, or content block), simply check the box next to the item and select the "Actions" dropdown. You will be presenting with a window with some settings.
Allow others to edit - If selected, this would allow other team members to edit the original item. If unchecked, they would simply be able to use the template to start a new proposal, but they wouldn't be able to update the "Master" version of that item.
Allow others to duplicate - If selected, this would allow other teammates to be able to make their own copy from this template within their library.
If you simply want to share the item, and your team members don't need edit of duplicating privileges, simply hit the "Update Sharing" setting, and the item will then be shared. And will show as "Shared - View Only".
Sharing folders is similar to sharing individual items. But, when a folder is shared, all the contents inside that folder are automatically shared as well. So instead of sharing all your templates individually, it could make sense to put all your templates in a folder, and then simply share that folder.
What your teammates will see
Your teammates will see a "Shared With Me" folder now inside their library where they will see and be able to access all the templates (or sections, line items, or content blocks) that have been shared with them by other team members.
How do I un-share something?
If you would like to remove sharing from any item, you can simply select "sharing" from the actions menu and click the "Remove Sharing" button.