Drupal 8.x

hello I want to create a content type as usual than want to create a module that on save manuplate existing field's values than put extra fields to form and save it. for example

Name
Body
Height
Weight
---------
Index = Height / (Weight* Weight);

what tutorial or book I should read to accomplish this. Please help I have been struggling about a week to find a tutorial.

I have just installed Drupal and I have made a few pages and articles. Suddenly I am not able to make any changes to existing articles nor make new ones. I am logged in as admin. I have tied to log out and in again. Have also tried to regenerate permissions. Nothing has worked. System info:
Drupal 8.1.0
Access to update.php Protected
Configuration files Protected
Cron maintenance tasks Last run 44 minutes 23 seconds ago
Database system MySQL, MariaDB, Percona Server, or equivalent
Database system version 5.5.5-10.1.13-MariaDB

Hello

I have a few D7 sites done, but now I decided to look at D8 as I love Twig (earlier used it only in my non-drupal web applications).

I have a proof on concept D8 site almost ready, except for one annoying problem (plus a menu that I haven't yet even looked at).

I have added a new multi-line html text field (let's call it field_right_column) to a plain vanilla Page content type and overridden the page.html.twig. The idea is that the user may lei it be empty or edit the column freely (as there seems to be no logic what is pushed there :P)

I need help programming a drupal site having this about functioning
Well there be some three databased objects about Student, Course, Classes and the main one Student Course,
I should deelop it by Drupal Module Development,

If there is anyone who could help me getting that on on a shared screen or on skype that would be brilliant - I wish to learn

I will pay some good drink in advance over paypal for whom helped me if you wish.

Hi is it possible to use date time field but only date field is required and time field optional? Thanks.

I'm using Drupal 8.0.5 and I would like to use date field with datepicker but I don't know how to do it. When I try to manage my date field (in Manage form display) there are only 2 choices "Date and time" and "Select list". can you help me. Thanks.