Two seasons after you issue a Call to Arms (CTA), the troops will be available to you at the fief you designated. When you go to that fief, you use this command to pick up the troops. If you don't pick them up on the season they are ready, the troops disappear (with a risk they will turn into brigands .) If the fief you have the CTA troops appearing at is, in the meantime, captured by someone else, the troops never appear for you to pick up.