When you first start using a Linux desktop, installing software might seem like a foreign idea. In Windows you generally get an EXE file or a setup file that you click on then follow the steps until it's installed. In Linux it works a bit differently because it is a different operating system.
Awhile ago you had to do something called compiling to get your Linux software to work. This is too complicated and pointless because it takes too much time and is really only for experts.
Now there is something called a Synaptic Package Manager that you can use to install Linux software. Most popular versions of Linux will have this type of program to make installing software easy.
Open up your package manager and you will see a search bar. Type in what type of software that you are looking for. If you need an html editor for example, just type in "html editor". You will find a list of sometimes a few and sometimes hundreds of options.
Select the programs you want to install by either right clicking and marking for installation or checking boxes. Hit Apply or OK and watch the software download and install automatically.
Then in your applications menu, you will find your new free software. You can try it out as long as you want. If it's not what you are looking for you can go back to the package manager, uncheck that version, and install something else.
What is nice is that there are so many thousands of pieces of free software that in many cases you will find exactly what you want to complete whatever task you are thinking of.