surface.SetFont
Example
Draws 'Hello World' on the screen, with the 'Default' font.
hook.Add( "HUDPaint", "HUDPaint_DrawABox", function()
surface.SetDrawColor( 0, 0, 0, 128 ) -- Set color for background
surface.DrawRect( 100, 100, 128, 20 ) -- Draw background
surface.SetTextColor( 255, 255, 255 ) -- Set text color
surface.SetTextPos( 136, 104 ) -- Set text position, top left corner
surface.SetFont( "Default" ) -- Set the font
surface.DrawText( "Hello World" ) -- Draw the text
end )