language agnostic

Generally speaking, there's no five minutes tutorial for compilers, because it's a complicated topic and writing a compiler can take months. You will have to do your own search.

Python and Ruby are usually interpreted. Perhaps you want to start with an interpreter as well. It's generally easier.

The first step is to write a formal language description, the grammar of your programming language. Then you have to transform the source code that you want to compile or interpret according to the grammar into an abstract syntax tree, an internal form of the source code that the computer understands and can operate on. This step is usually called parsing and the software that parses the source code is called a parser. Often the parser is generated by a parser generator which transform a formal grammar into source oder machine code. For a good, non-mathematical explanation of parsing I recommend Parsing Techniques - A Practical Guide. Wikipedia has a comparison of parser generators from which you can choose that one that is suitable for you. Depending on the parser generator you chose, you will find tutorials on the Internet and for really popular parser generators (like GNU bison) there are also books.

Writing a parser for your language can be really hard, but this depends on your grammar. So I suggest to keep your grammar simple (unlike C++); a good example for this is LISP.

In the second step the abstract syntax tree is transformed from a tree structure into a linear intermediate representation. As a good example for this Lua's bytecode is often cited. But the intermediate representation really depends on your language.

If you are building an interpreter, you will simply have to interpret the intermediate representation. You could also just-in-time-compile it. I recommend LLVM and libjit for just-in-time-compilation. To make the language usable you will also have to include some input and output functions and perhaps a small standard library.

If you are going to compile the language, it will be more complicated. You will have to write backends for different computer architectures and generate machine code from the intermediate representation in those backends. I recommend LLVM for this task.

There are a few books on this topic, but I can recommend none of them for general use. Most of them are too academic or too practical. There's no "Teach yourself compiler writing in 21 days" and thus, you will have to buy several books to get a good understanding of this entire topic. If you search the Internet, you will come across some some online books and lecture notes. Maybe there's a university library nearby you where you can borrow books on compilers.

I also recommend a good background knowledge in theoretical computer science and graph theory, if you are going to make your project serious. A degree in computer science will also be helpful.