When installing Sytist, you should first decide where to install.
On your web hosting, you have a main public folder ... also called the "root". This is where you main website files are located.
1) Install in the root of an existing website.
You can install Sytist in the root folder of an existing website and not effect your current site. This is because by default the index file is named indexnew.php. This means it won't override your current index file and not take over your website.
You can choose this option if you plan on making Sytist your main website. When it is time to go live, there is a link in the admin to do so which will backup your index file and rename the indexnew.php to index.php
If you are not going to be using Sytist as your main website, select one of the 2 following options.
2) Install on a sub domain
A sub domain is like folder-name.mywebsite.com. You can leave Sytist on the sub domain and use it just for selling or eventually move it to the root to make it your main website.
3) Install it in a sub folder
Installing on a sub folder would be like mywebsite.com/folder-name . You can select this option if you are not planning on making Sytist your main website and use it just for selling.
You would also select this option if you are installing on a cPanel temporary url (which is like 123.45.65.125/~username)
See this page on how to install in a sub folder.
4) Installing on a clean website with no content.
Super easy, no worries.