I want create my Mosaico template in WordPress with the CiviCRM extension but I can't find where upload the new template.
Secondly, must I activate the new template after uploading it to my host?
As you can see on Mosaico Extension v2.0-beta3, etal release, since this version...
In the CiviCRM menu, you'll find a new item "Administer => CiviMail => Mosaico Settings". This exposes options, such as "Layout" and "Custom Template Directory", which would otherwise remain hidden.
v2.0-beta3 allows site administrators to install templates in the "Custom Template Directory", and it allows developers to bundle templates into CiviCRM extensions
When you install the Mosaico and related Extensions, you then create the Templates in civicrm and they become available to use in CiviMail, you do not upload them.
If you have installed correctly, as per instructions, ie Shoreditch then FlexMailer then Mosaico then at /civicrm/a/#/mosaico-template you should see the word NEW on top of the base template
You can create a new template through following steps:
Hope that helps.