What software available in Linus is best for Newbies?

What application software is easiest to learn to code for Web Development for GUI and Backend development for Database Management?

Bluefish is a good HTML editor; arguably you need to learn MySQL/MariaDB which underlies most CMS applications but a lot depends on the particular things you intend to do.

Plus php, javascript. Personally - I’m old - I prefer Kate for working on webapps, and use the MVC ( Model View Controller ) model.
But f.e. Joomla sites seem to be editable fine in Eclipse.

Need a better detailed description of what you mean by “Web Development for GUI and Backend development for Database Management”

There is Web(site) development as a subset of all types of application development.
There is database backed websites as a subset of the above, and there are many types of databases to choose from.
The specific creation and maintenance of just the database used by the website has its own language and tools
When it comes to connecting the website to the database, there might be choices but most commonly pre-built components with APIs facing the website and on the other end facing the database are usually provided for you… This is because the website connection to a chosen database is usually standardized so there is less room for creativity how to do it.

For each of the above that specifies something very different from another,
You generally have to choose a website language to use, and there are many fans. Because all modern coding involves at least some copying or using re-usable components, it might useful to find out whether there are existing solutions or examples of what you are trying to do and what language they’re written in. Any code that you can re-use for your own project could be code you don’t have to write yourself.

When you have a general idea what is available, you should try some basic coding in various candidate languages to see if any are more preferable than others… You’ll probably have choices like HTML/Javascript/CSS, python, php, java, c#, maybe more.

Based on the above, only then I’d recommend you look for an IDE (Integrated Development Environment) to help you code. A couple I generally recommend for beginners that support a variety of languages are WebStorm (free or discounted for students) and the free and open source Microsoft web development tools (they change all the time recently). Be aware though that the “help” you get sometimes can be limiting so be prepared to change tools if you find a tool that doesn’t work for you. Linux has plenty of free tools too,but I consider most of them as usually enhanced text editors (which they often are) and do nothing for setting up organization and resource management(you have to do it yourself without guidance). When you’re a better coder who knows how to organize your resources and might need less help, enhanced text editors can be your best tools… and maybe when you get really good, top coders often use a regular text editor with almost no enhancements.

Another consideration might be if you plan to ultimately deploy on a cloud service. If this is something that is set from the beginning, then some cloud providers are more suitable for one language over another (eg Google Cloud has special support for python, Azure has special support for dotNET). And, some database engines are available or not on each Cloud.

TSU