the easiest way is to use a finish to finish (FF) constraint. this will ensure that task 2 always finishes at the same time as task 1, while allowing the start date to move if necessary (see pic )

It is important to note that task 2 must be a successor to task 1 for this to work (ie you work downwards).

I did look at your link, and frankly it seems to be written by someone that hates Project. I started on Project and overlapped with P6 for 4 or 5 years, and now have to us P6 for most of my work. People going from P6 to Project tend to expect things to work as in P6 and if they dont, assume it isnt there.
If you stick with Project, you will find its actually a lot better than it gets credit for. Its just a case of learning the software, and it will come

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