Joking aside, I´m gonna explain it in this forum. Ari, "lighting" isn´t exactly the right sub-forum to discuss a lightmeter. ;-)
The german manual can be found at
http://www.gossen-photo.de/pdf/ba_sixtomat_d.pdf
The blinds act as a diffusor, but the material has a tendency to yellow during time, making it useless.
Looking at the window frame, you´ll see three lines - a fixed horizontal line and two variable lines. One of them is a pointer that moves in relation to the amount of light hitting the selenium cell.
Set your film speed, point the lightmeter to the object and watch that needle pointer move, then turn the dial. The third line will start to move, you´ll have to line it en par with the point the two other lines cross each other.
Thats it, now you can read your shutter/f-stop combination from the table above.
Most of those 1950 Gossen lightmeters actually work. Despite common rumour, selenium cells don´t fail that much due to "abrasion" from incoming light but due to oxidation.
The selenium cells need to be laquered to protect them from oxidation and the quality of that film impacts the "useful life" a lightmeter has - thats probably the reason why some types like the old Westons, the classic Gossen Sixtomat and old soviet Leningrad 2 lightmeters from the late 1950s still work fine despite their age while other types fail after only a few years of usage.
An other common "point of failure" is the copper contact plate behind the selenium cell - they tend to corrode, too.
BTW, there are still few new cells available from Russia, designed for Zenit SLRs, but they should fit many classic meters and cameras. A company in England is selling new cells, too, but at prohibitive cost.
