from scratch, in notepad++, vscode so on... basically writing a bunch of features and uh... layouting the folders, doh H dot cpp files dot ini (kernels, system file, whatver) and compiling to finish, ready use exe or apk...
especially building/enabling the network, multi user controls&connection&interaction, storing user data...
what book/tutorial do i read/watch? or maybe what do i type in code, or extension to install