In Zenless Zone Zero there are two types of banners that change regularly, so you can pull at different times for different Agents and W-Engines. Here is the full Zenless Zone Zero banner history back to 1.0 so you can see what you missed.
Beginner's Guide to Zenless Zone Zero Lore 【ZZZ 1.0】
There are two types of Agent banners (or channels): Stable and Exclusive. Normally you should primarily focus on the Exclusive banner, as these Agents are usually not available for pickup on the Stable banner (unless they are added).
The exclusive channel guarantees an A-Rank or higher signal in 10 searches and an S-Rank signal in 90 searches. If the agent you want is on the banner, you should save the Encrypted Master Tape in the hope of getting sympathy.
Don't worry, the exclusive banners will stay up for about 20 days. That means you have plenty of time to prepare for the draws (and you can even skip a channel if you know the agent you want is coming soon).