We don't have the T tool anymore. So you're faced with a couple options...
Zooming all the way out (shift z) and selecting with the standard FCP/macOS marquee, shift and cmd click methods. Unlike FCP 7 you only need to select what's in the primary though, since all the other clips are connected to them. If you're looking to move them down the timeline into empty space you'll need to use the P tool.
Or if you just need to make space by moving everything down, that's as simple as pressing option w to insert a gap/slug which you can then drag out to the desired length or select and choose cmd d and type in a duration. Since everything is connected to the primary, inserting a gap into the primary moves everything down.
But just like FCP 7, be aware of clips that overlap the insert point. They are most likely connected before the insert point so they won't move. So if it's important that some music end at a certain spot, you might want to connect it to the primary toward its end. (Cmd+opt and click on the clip where you want the connection point). Or before making space you can split everything so it all is sure to ripple down. That's shift cmd b.
Too much info? Just answering your next questions. :)