"These operations seem to require definining new variables separately? Is it correct?"
No. It is very very rare that coding in any language "requires" one specific approach to a task, in most cases you have many approaches for solving a particular task. Understanding which approach/es will be simpler, more efficient, easier to maintain, etc. comes with practice and experience and reading the documentation and continuous learning. In general, following the good practices for that particular language will go a long way to helping you down that path.
There is nothing in your example link that "requires" separate variables, and that would be a very inefficient approach for a larger number of variables (both in terms of runtime and writing/maintaining time), basic indexing would be a much simpler and more effiicient approach.
A common mistake that some beginners make with MATLAB is wanting to split data up into lots and lots of variables, but this makes accessing and processing data more difficult and much less efficient.
