So you go and build "Senat" to Level 4, same with "Bauernhof". When you did that "Kaserne" appears in the "Senat", ready to build. Build it and you can recruit "Schwertkämpfer". Click on "Kaserne" and just choose how many you want, finish with clicking on "Rekrutieren". After a short time they will be recruited in your village.
For new units build an "Akademie" also, it needs Senat: Level 8
Bauernhof: Level 6
Kaserne: Level 5.
With it you can research new units like "Hoplit" or "Reiter".