Tersus Studio is all you need to get started. If you look closely you'll notice that in spite of the fact there are multiple links, there are actually only 2 products: the studio (for development) and the server (deployment), with the links targeted at different platforms and versions (stable vs. latest).
There's no way to search a specific forum, but note that each search result displays its source/location, which helps in deciding whether the result is relevant.
Tersus provides 2 versions, an open source one and a commercial/enterprise version which expands on the features provided by the open source version - see http://www.tersus.com/#Id=279.
There are various options with regards to changing the button caption. You can rename the element in the model (select the button and right-click>Rename or F2), or you can add a <Caption> text element and use flow to change the caption dynamically. If you've just started I guess both options seem rather cryptic, so I suggest you continue with the Tersus Tutorial as recommended at the bottom of the welcome page.
For best results, use the Firefox browser..