Thanks for your comments. As author of this article, I am happy about each reader of it. But please consider, this is a STM32/ESP8266 article and not a Lazarus one.
So I added this PC client as a service to the readers and have provided just the Exe into the project. It is a useful utility, which acts as TCP/UDP server and client running with IPv4 or IPv6 using optional SSL.
If you want to extend the functionality with source modifications, you have to perform the following steps:
1. Download and install Lazarus and FreePascal
2. Download and install the component INet
3. Download and install OpenSSL
In the INet package you will find a Lazarus project called testnet including all sources and forms. This could be the base for you for your own projects.
Have fun with your projects!