You already know how to program, but lets cover the basics quickly. In addition comes some specific comparisons to other programming languages.
Syntactically, D looks very much like C/C++/C#/Java. There are the keywords like if, while, class, struct, int, double, private with unsurprising semantics.
For C (and C++) Programmers¶
D has no preprocessor, but equivalent meta programming mechanisms.
Syntactically, most C code is actually valid D. It should be noted that D defines a lot of things, which are undefined (or architecture-, implementation-defined) in C. For example, integer overflows wrap around in D, because that is what practically every architecture today does.
For Java Programmers¶
D provides classes, interfaces, modules, packages, and a garbage collector. This should make you feel at home quickly.
D programmers care a lot more about efficiency, which means there is a lot of machinery to improve performance.
Instead of Java Generics, you have D Templates, which cover similar problems, but have different syntax and semantics. Read about that carefully.
For C++ Programmers¶
You should generally feel at home. If you enjoyed the C++11 innovations, you will find similar stuff in D. D even has things which were dropped from C++11.
Prepare for some syntax changes, though. D is not burdened by C-Syntax-Compatibility. However, you can link C and C++ libraries, if the header files are ported.
For C# Programmers¶
Lots of similarities and various differences. While you should feel at home, D does various things different and that will take some time to adopt.
Instead of a syntax extension like LINQ, D provides a lots of similar mechanisms in the standard library.
D is statically typed, which probably takes some time to get used to. However, D really tries to let you skip boilerplate. Declare your variables with auto or const.
auto x = 42; const y = "yes";
Also there is Variant, which can be used to put anything into a variable.
The D standard library strives to come with all batteries included. Unfortunately, D is not as mature as Python. While it is possible to be as terse in D, often the libraries are missing for small scripting jobs. You can use C/C++ libraries, but that does not feel like batteries-included.