Hellow and Welcome,
here you can see some first steps to get into the game.
For some buildable things you need to craft a Workbench. The Workbench does have some slots too to save some of your Items.
To get interact with - you press "TAB" and then the interactionmenu appears. Then you get in contact with your mouse and select your action then press "Spacebar"
If you fall down from some building then you have luck and you fall into unconscious. Then you have to wait a little time to wake up.
The Interactionmenu for Client
Press "I" for Interaction/Craftmenu