Use the word sequential to describe something that has a particular order, like a recipe for chocolate chip cookies whose steps must be followed in a sequential order.
If you make a list of things you need to do, starting with number 1 and continuing until all your tasks are accounted for, then you’ve made a sequential list. Something that is sequential often follows a numerical or alphabetical order, but it can also describe things that aren’t numbered but still need to take place in a logical order, such as the sequential steps you follow for running a program on your computer.