How can I start to develop in SharePoint Online

[c03945]

Hello,

I'm programmer and I want to migrate the intranet's page of my company to sharePoint Online. My company paid a specific course offered by Microsotf, but de content was very very bad.

I need to start to program to make same aplications and I don't know what is te best and haw can start.
I'm researching AddIn.
Can anyone guide me or send me information to start developing custom applications in SharePoint Online?

Thanks.
Regards. 
Belén

[#2]

@c03945 Try looking through here https://developer.microsoft.com/en-us/office/blogs  However, before creating SharePoint add-ins consider your company's Office 365/Microsoft 365 licensing and what other apps are available for you to use out of the box.  It is so much more than just SharePoint now and you maybe able to use functionality in other Apps (Teams, Planner, Power Automate etc..).  Also SharePoint has a number of Web Parts already available Out of the Box.  Have fun there is so much there to use.