Drupal 8.x

Someone could explain me what is the function of the .module file in a custum module?

Thanks!!!

I found an answer to this for Drupal 7 dated July 2015.  It should have worked in Drupal, but I certainly can't get it to work.

What I am trying to do is create a view on my front page that is a gallery (grid) of images.  I am using Commerce2 and I would like to use images from a particular product type in the grid.  When someone click the image, I want another view with a gallery of particular category to appear.  Obviously, if I set the image link to Content, the visitor will be directed to the Product page - not the gallery view.

I have a Drupal 8 project that was created with composer create-project drupal/recommended-project web when drupal/core version 8.8.3 was the latest version. Updates has been managed with composer ever since (composer update 'drupal/*' --with-dependencies).

I assume that the whole idea behind using composer to manage a project is that it is supposed to automatically keep all dependencies in sync.

Is it possible to schedule an alert after a node is saved. For example, a user creates a node and completes fields requesting an email or SMS alert on X date at Y time. I was hoping to use rules scheduler like there was in D7 but I cannot find it in D8. Any help appreciated.

I'm running Drupal 8.9.3.  I have some content types are rather large, so I'm using field groups to put related fields on different tabs.  If a user forgets to fill in a required field on the first tab and presses save, a bubble pops up saying, "Please fill out this field."  However, if I switch to a different tab and press save, nothing happens and there is no indication as to why it isn't saving.  These pops only seem to work on the first tab and none of the other tabs.  I've tested this in both Chrome and Firefox.  I've also tried different admin themes (Seven & Claro) to make sure i

I've created an additional CSS theme for the sub module while the primary front-end dev is working on style.css. Following the excellent docs, particularly all pages, these two CSS files show up on the home page, 404 page. But my ancillary.css does not appear on localhost/taxonomy/term/86/edit where I'm looking for it. 

#mytheme.info.yml