Display serverside variables on clientside

I have this DLabel and I want the text to be self.propane, self.propane is a variable in the serverside file. How would I make it work?

Network this variable with SetGlobalInt, SetNW* or just network this once with net messages

I have this:
[lua]
self.propane = 100
SetGlobalInt( “propane”, self.propane )
[/lua]

and this in clientside:
[lua]
local labelP = vgui.Create(“DLabel”)
labelP:SetParent( mainFrame )
labelP:SetSize( 150, 15 )
labelP:SetPos( 400, 240 )
labelP:SetText( "Propane: " …propane )
labelP:SetFont( “nFont1” )
[/lua]

But it says it’s a nil value.

What’s a nil value, and is it on the serverside or the clientside?

Also where is the serverside located, is it inside an entity?

Use SetNWInt if you are using entities.