Waves and Syncing

Each building releases troops on its own cycle (the spawn bar of the selected building). Sync (S, then click the parent, whose timer is equal or longer) makes the child spawn together with the parent: troops come out as a wave. Pause (A) freezes the bar so you can time it by hand. The flag (F or right-click next to the building) picks which side troops spawn on, even inside a cage.

Spawn cycles

Every troop building has its own spawn time. Select one and you'll see its bar fill; when it's full, a troop is born. A new building releases its first troop halfway through the cycle. The selection panel also tells you when the next troop comes out and whether the building is synced or paused.

Because each building runs on its own clock, troops left alone come out a few at a time. A wave is what you get when several buildings release together.

Syncing

Select the building you want to sync (the child).
Press S.
Click the parent: another troop building with an equal or longer spawn time.

From then on, the child spawns together with the parent. Good to know:

Syncing resets the child's spawn bar and its spawn flag.
If the parent is slower, the child now trains on the parent's slower clock, so you get fewer troops in total. That is the price of the wave.
You can sync several buildings to the same parent. Syncing to a building that is itself synced links you to the head of its group.
To undo, press S and click the building itself.
If the parent is destroyed, its children go back to their own cycles.
While the parent is upgrading, the whole synced group pauses production.

Syncing is optional: the Training presents it as a tool, not a requirement. Use it when you want your troops to hit at the same time, the way a synced enemy does.

Pausing production

A turns a building's production off and on. While it's off, the spawn bar freezes. That's the manual way to line buildings up: pause the ones that are ahead and turn them back on at the right moment.

Reading enemy waves

When the enemy syncs, its troops arrive in groups instead of a steady trickle. A big group heading for your base is exactly what the Rescue is for. As the Wave timing lesson puts it: troops spawn in cycles and arrive in waves, and the same Rescue is worth 2 kills or 10, depending on timing.

The spawn flag

With one of your buildings selected, press F (or right-click the ground next to it) and click the spot where its troops should come out. The building uses the nearest free tile around it. Click the building itself to go back to automatic. The flag is how you fill a cage on purpose: see Shop, perks and cages.