Now that you have a new map, go to the "new item"
button, as you click that another window with a list of thing will show up.
How to make an arch ?
Step 1
The first thing you do is start up QuArK and make sure you
have it set to Half-Life.If not this can be done by selecting
"Games"
and just scroll down to Half-Life.
Step 2
The next step is to make a new map. This can be done by clicking
the button above.
Step 3
Step 4
Now, go down to "Shape Builder" double click it. Then
you will see 3 more items show up,
double click "Brush Arch/Cap Maker"