Turning a plan into instructions
Once a team has agreed on a feature, developers use its tickets and technical design to decide what the software should do. They write source code in files using a programming language such as JavaScript or Python. For an online shop, that might mean instructions to calculate a basket total, check a discount code, and show an error when payment fails.
Source code is usually text that someone familiar with the language can read and change. Names such as basketTotal help explain what a value means; functions group instructions for a task. The code still has to follow precise rules, so it is not simply a description in everyday language.
From source code to a running product
A computer’s processor runs machine instructions, not the source files as written. How the source gets used depends on the language and platform. A compiler may translate it before the program starts; other software may interpret it or compile parts while the program runs. Either way, machine instructions ultimately do the work.
Saving a source file does not change the product people use. Developers try their changes in a development environment, test them, and record them in version control. Later steps build and release a version that people can use.