How computers understand programming language ?

Answer 1

they get parser using the languages grammar to check if the code is valid.
then it can be converted to code your computer can work with aka 1s and 0s

Answer 2

Or, alternatively, if the program is interpreted (like Python), another program (which is 1s and 0s) reads the code and executes it instead of it being executed directly by the processor. That's important for languages such as JavaScript: the server feeds the code directly to the browser, which then executes, instead of the server executing the code and then feeding the result to the browser.