Drupal 8.x

I am a seasoned developer in many languages and looking to get started with Drupal development. Where can I get the best tutorials or video lessons to get started. Your help is well appreciated.

in Drupal 8 I have a content type with a text field, and two image fields. The Field Type for each image is 'Image'.
In Views I have selected these fields to be displayed as a Page.
In the image Field Settings, if I change the Formatter from 'Image' to 'Responsive Image' both the default choices 'Narrow' or 'Wide' go red, and show this error:-
"An illegal choice has been detected. Please contact the site administrator. "
This happens with all choices for Format of the Page (Grid, Table, HTML etc.)
Any ideas why this might be?

So I've successfully managed to install Drupal 8 in a sub-directory. The problem is I haven't figured out how to correctly redirect /user to /sub-directory/user. Currently I get the following error:
Redirects to external URLs are not allowed by default, use \Drupal\Core\Routing\TrustedRedirectResponse for it.

There were several other topics that I found on this that recommended adjusting the trusted_host_patterns in settings.php, but I have already done that (prior to noticing the error).

Hi!
I just triyinf to import a CSV file to create a taxonomy data on my Drupal 8.2.5.

That is the CSV file content:

Name,Description
"Name1","Title1"
"Name2","Title2"
"Name3","Title3"

This is my taxonomy categories
field_description
field_category_name

And my .yaml file has:

Hello everybody, hope ya'll are having a great day and I hope that you can help me or point me in the right direction.

I am using one of the Drupal's free themes. What I have to do is to create a new page called, let's say Service ( domain.com/service/ but the catch is that this page needs to have a different header and footer than the rest of the site.

I've been searching for information on how to do this quickly and easily and i couldn't find anything to help, or maybe i didn't searched properly.

Any help will be greatly appreciated!

Thank you all.

Hello all,
I´m trying to notify other users if a user goes offline using Node.js integration module.

I found a method called nodejs_user_set_offline in the .module, is it possible to get this information into my module without altering the code of the module?

thx