To longtime collectors of course this is perhaps old news, but it can be confusing to new collectors. I’ve come across several of the J. Crew Timex “Military” watches in the wild where the owner has simply cut off the excess and wears the strap with the tail tucked under the keepers. While effective in a sense, this method is not the most correct and also gives up part of the advatage of the G10 design that would allow it to be resized for wear over coats, wetsuits etc.
Bill Yao at Mk.II Watches has a pretty great illustrated guide that shows how to attach the watch to the strap.
It might seem complex at first, but it requires only a bare minimum of practice and once you’ve managed it one or two times it becomes second nature. ZULU and RAF-pattern type straps are worn using variations on the same technique shown here.
Pro tip: when putting the strap on your arm, it’s often helpful to lay the watch on the wrist and the press your wrist to your chest while you thread the tail through the buckle and keepers.