I just watched it. I don't understand, what to expect - for example, in the songwriter are the same software instruments as in the new project. Where is a difference, what I can expect more with songwriter, than with a new project? Also keyboard project looks quite similar to a new project.

There are no rules. GB's Templates are just Apple's suggestions of what instruments/sounds they think might be useful to someone doing a song in a particular musical style/genre -- if the Templates don't suit your workflow then just ignore them. Most people just start with a blank Project and choose whatever Instruments/Tracks they want/need for that particular song.