How do you build tools on roblox

In studio, without anything selected go to the Insert drop-down menu (next to file, edit, view) (not next to tools, fullscreen etc.). Double click tool (or some tools work with hopperbin). Tools have a part in them called "Handle" (spell like that). Handle is the "face" of the tool, the thing you see your character holding. For the rest, you can add in scripts and stuff. There are lots of different tools in Roblox, so I suggest you check out what the Roblox wiki has to say about it.