Question about building a castle tutorial

Is there somebody can explain how we can make a door in the wall … I did not understand how can I use the box select ( is it by pressing B key or what ? ) and which vertices should I select … can you help me please .

You mean “how to make the gate”?..
Great a circle, then press “B” and select
the cirlce beneath, so you’ll get a half circle.
(All in edit mode - TAB)…You’ve already created
a plane,…remove the bottom of it (also in edit mode)
then right click one (gets yellow) of the vertices of the ‘half’ plane and
then you can add more vertices by holding the “CTRL” key and press
“Left mous button = LMB”, create the walls until you get under
the half circle,.right click on the last created vertex and hold down
“Right shift” and click with your “RMB” on the first vertex of the half circle
and press “F” this creates a face,…the same steps you’ll do at the other
part of the plane and attach it to the right part or left part of the circle,…
then select all the vertices with “a” en press “CTRL+F”…
The plane and circle must be in the same edith mode,…
so the cirlce and plane must be purple, or when selected yellow…

Hope it’s helpfull to ya!

Enjoy Blender, and greetz

It is very helpfull
Thanks snowboarder