To start, navigate to Templates choose New Template > Create video template
In this example I am going to change the format of my template from the default 1:1 to 16:9 to match the assets that I want to use. You can do this by selecting 'Formats' on the right hand side:
You will see the timeline in the lower portion of the screen along with buttons for 'Main Sequence' and 'Scene 1':
In this example I want to add two video clips from my Asset Library - Scene 1 and Scene 2. To add your first video asset click on 'Scene 1' and then click on 'Assets' on the left hand panel:
From here you can select the video asset that you want to use. You can choose from your Asset Library or you can directly upload video assets. The asset will appear in the Scene 1 timeline as well as in the main template canvas, where you can resize it if need be.
Going back to the 'Main Sequence' view I can see my 2.7s video clip and, after it, a 'plus' button which allows me to add a second scene. Repeat the process above to add a second scene containing a second video asset:
You can continue to add video assets in this way, use the editing functionality, as well as the pre-built transitions and animations.