[newbie] organize widgets in columns in a template form

I am learning template form. I have autocreated a form, converted in template form clicking a button and now I would like to rearrange widgets.
How can I move several widgets on the same row? I am trying to add columns but also columns are put on next row.
Probably a little video on the new template form would be useful.

Total number of Bootstrap columns is 12: https://getbootstrap.com/docs/4.0/layout/grid/, you can change the Size if you want to have more than one column: