How to set tabs on an old Adler typewriter?

I don't know what model this is. I just borrowed it from someone who doesn't use it for a long time. It's a large format typewriter with a Philippine keyboard(with a Peso sign). It has a tabular button with two buttons beside it(- TAB +). The + is hard to push down but the - can be pushed down. When I press the TAB fully down, the carriage just moves to the left, past the right margin. Then it stops at the very end of the carriage. How do I set the tabs?