How do you weld bricks on roblox?

Got to the bar across the top of the screen while in Studio, and click on "insert". Select "Basic Objects" from the drop-down menu. This will bring up a list of objects on the right hand side of your screen. Scroll to the very end of the list and select "weld".

If you don't see the "weld" at the end, try deselecting whatever object you are on, and putting a weld in the Workspace. Cut and paste it from the Workspace to whatever object you want it in.