I haven't played Stepmania in ages, but let's see if I get this right.
The file opens in WinRAR most likely because it's a RAR or ZIP file, which basically means it's been compressed and sent as a single file when it's actually multiple files. If it's an individual song, the RAR/ZIP file should have things like the mp3, the step chart, and the banner and background images in it. To put it into the game, you have to go to your stepmania directory (generally C:\Program Files\Stepmania if I remember right), then go to the Songs folder. Here it's kind of strange -- you can't just put the song here, you have to put it in a new folder. If it's a song from a DDR mix, you could make a new folder called, say, "5th mix" and put the files in there. They have to be inside their own folder inside the 5th mix folder, though.
So basically, it should look like this: Stepmania folder --> Songs folder --> 5th mix folder --> Folder with the name of the song as the filename --> mp3, step chart and banners.
In the future, questions about Stepmania should go on the "Dance Dance Revolution Simulation" forum (there's actually a stickied post there that explains how to add simfiles to Stepmania).
As for tokens, you can use them for things around the site, such as changing your username, altering its color, etc. At the top of the page, go to Forum --> Shop --> Main to see the different things you can get with tokens. | 
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