This is the entire framework, and everything else in the program is an application of it.
1. Find
Take one set inside the tier's range. Not a prescribed number of reps, a range: you take the set and see what you get.
A T1 set is 3 to 6 reps. A T2 set is 6 to 10.
2. Extend
Back that set up at the same weight, with the extension derived from what you just did.
T1 extends with singles, one per rep you managed:
You got 5 reps on the find set
-> 5 further singles at the same weight, 2 to 3 minutes apart
T2 extends with half sets that double the set's volume:
You got 10 reps on the find set
-> 4 sets of 5 at the same weight, so 20 more reps
If the find set felt easy, add up to three more singles on a T1 or two more half sets on a T2. That is your call on the day and nothing else in the program depends on it.
3. Hold
The next session, repeat exactly. Same weight, same rep target, same extension. This is the step people skip and it is the one that makes the framework work: you are consolidating a rep target before you try to beat it.
4. Push
The session after that, go for one more rep on the find set. If you get it, the extension grows with it.
And Then the Weight Moves
Reaching the top of the range with every extension set completed adds weight and drops the rep target back to the bottom.
T1: 6 reps + 6 singles -> add 2.5 kg / 5 lbs, back to a 3 rep target
T2: 10 reps + 4 x 5 -> add 2.5 kg / 5 lbs, back to a 6 rep target