i am new in gog world and galaxy thing. i cant install my free games why ?

Galaxy is still in Beta and a lot of games still need to be repackaged in order to work with the client, I'm assuming it's the case with Teenagent and other free games.

For the time being, I'd recommend installing GOG games the old fashioned way -- downloading them directly from your library, with or without GOG downloader -- and running the installer manually. Give Galaxy some time until it performs a bit better, as it is now, it's not very good a product and feels a bit rushed.